You mention Arsenal in MGS4 and I agree with you about that being a great area in that game, but it's a prime example for showing why MGS5 is even better. In MGS4 the frogs are scripted completely, they will always appear when you hit certain points. Basically the game cheats, and you can't out-plan the enemies until after you trigger them.
This type of AI cheating is all over MGS4 and MGS2 to a lesser extent. Like the enemies spawning forever CoD style in Act 1 and Act 2. Stealth an area but then, oops- time to infinitely spawn more enemies directly in front of or behind Snake. This is aggravating as hell. What's amazing about MGSV is doesn't do that type of scripting with very few exceptions (usually involving prisoners). Guards have patrols they go on without the psychic AI bullshyt. And the areas are just as tense to sneak through. If a guard comes through and finds a body it's because it was a long range recon patrol that always would, or a set shift change that'd always occur regardless of where the player is. This is brilliant because it allows one to plan, yet also be surprised by enemies in a fair way.
I know this is a thread for the controls, but since a lot of people aren't staying just to that topic I just gotta say:
MGSV doesn't get enough credit for how great the systems of AI it has work, and how it juggles them. You have tons of AI soldiers in an area, with great reactions to pretty much everything the player does. From firing a silenced gun, seeing missing supplies, missing vehicles,
seeing a box move, etc. The AI also multitasks. If a soldier thinks he sees a suspicious individual, and then hears a noise he may look in the noise's direction briefly, but then will go right back to investigating the more important suspicious individual rather than forgetting about them (like GZ and previous games). On top of that it also is keeping track of the AI on long patrols, and state of alert in other bases.
Just having all that would already make the game great AI wise. But there's so much more. There's other AI going, AI buddies are all pretty great. And the enemy AI can actually see them, no Last of Us style invisible buddies here. If the soldiers see Quiet they'll react,
same if she knocks someone down while traveling. You can recreate the scripted CoD "you take the one on the left, I'll take the right one" at any time. D-walker will be destroyed on sight. If the enemies see d-dog they'll shoo him away. If they're searching for Snake they'll ask "Hey boy, smell someone?", or if d-dog charges they'll react accordingly and shoot. There's multiple levels to each interaction accounted for and it makes the game feel great to interact in. Sure D-dog will run around and into guards as a big dog would, but you can tell him to sit and it's pretty minor considering the amount of ground and obstacles he and Snake can traverse. This interaction continues with the wild animals around. The AI will engage each threat accordingly, and separately. This allows the player to use the animals, buddies, and helicopter to all be diversions.
And one more thing, having a separate alert and combat alert is brilliant and makes that possible. It works a lot better than the way MGS4 shoe-horned the old one into its battlefields. And even if one uses a weapon and shoots at enemies from a distance and are not seen, if you keep firing they'll pick up on the location the fire is originating from blindly return fire even if they don't know for sure the player is there exactly. It's a lot more fair then them just knowing like the old games and getting an alert while still offering some resistance to just sniping everything. Oh and how the enemy fights in a combat alert is also great, once Snake breaks line of sight they will assume he's in that area, they won't psychically know if he went somewhere else unless they see him go there. Watching them shoot the hell out where I used to be while sneaking behind them is a thrill. Things like decoys give great ways to test and explore this.
Combine these controls and AI systems and you've got something that is fun to play regardless of environment. That said,
I'd put the level design of the bases in mission 3, 4, 6, 9, 12, 13, 16, 28, 30, and 35 up against any of the areas in MGS4. MGS4 offering similar advances in tech, similarly large areas, and being known for similarly good level design as the previous games.
In fact, let's compare the traveling through the power plant area and mansion to the Laughing Octopus battle (arguably the best of the beauty core) in Act 2 of MGS4 to Mission 6 "Where the bees sleep" in MGSV. So the areas themselves are similarly large and filled as many nooks, hidden goodies, and secret paths. Both have small buildings that can be entered. The rewards for exploring those areas in MGS4 are chaff grenades, prisoners to save, ipod tracks, and guns. MGSV is similar and saturated with rewards like radios, soldiers, prisoners, diamonds, and materials. They've got the same patrolling helicopter and heavy enemy presence, etc. Although mission 6 does without the bullshyt infinitely re-spawning like in 4.
If the player takes out the snipers on the bridge in MGSV, they accomplished something, same if they shoot down the helicopter. The game rewards them with less threats in the area and more points. If they extracted the soldiers, potentially new soldiers with cool skills as well. If the player takes out the snipers in the towers in the area past the power plant in MGS4, another one will magically appear 1 minute later and knowingly take the dead or knocked out soldiers place. One gets nothing other than the drebin points if for picking up his gun before he gets there. shytty risk reward there. Coming across the helicopter in mission 6, its patrol is actually a serious concern. In daylight it can easily spot the player if they're anything but prone. If it does get alerted and the player hasn't brought a missile launcher Snake is fukked in a fight. Unless they call in a launcher and avoid it in combat until they can retrieve it. If one manages to sneak by, it's a real relief. Take it out, and it really feels like something was an accomplished. The threat is removed permanently and the player get points towards rank and achieve a hidden side objective for it. Now let's compare that to MGS4's patrolling chopper. This might as well be a prop. It can't see Snake unless it's an alert. It doesn't even shoot at the rebels if I recall correctly. If the player decides to destroy it they effortlessly go into inventory, equip a missile launcher, and hit with ease since it moves so slowly. Then they get some drebin points. woo. Oh and then in another minute the same helicopter comes and takes it's place. :/
So okay, what about those prisoners? That's where MGS4 should shine given the emphasis put on the battlefield. In 4 prisoners are about to be executed. Sneak by or risk detection to save them. Saving these initial prisoners gets outfit and shotgun, pretty good. But past that the rebels come in to help whether saved or not, but still it's a good sandbox where the player gets to figure out how they want to save them. Saving further prisoners doesn't offer any reward, they will just run off screen or get shot immediately. Although, if Snake helps them take out the power plant (the only way to stop the infinite soldiers in that area) it'll leave have an extra path without enemies an access to a area with a stinger. Also a decent reward (well not the stinger, that's pretty worthless compared to the Javelin). Now to the prisoner in MGSV, sneak to the bridge and one can see him getting water-boarded and interrogated (this is actually the animation ripped directly from a cutscene in the e3 redband trailer, just with soviets instead of marines). Can choose to save him there by rushing over or can mark him and watch him lead me directly to the mission objective. The key difference here is this all very subtle, if the player doesn't carefully scope out the area they may never see this prisoner, it doesn't cut to a cutscene and throw the stakes in anyone's face. Rather, even noticing the prisoner is a reward for observant players. This is the thing that makes V so controversial. Some want that cutscene, they don't want to potentially miss a cool gameplay gimmick. Others like having to earn that intel, and become more engaged from knowing they found something on their own. In any case if tracked the prisoner he will eventually lead the soldiers on a windy path to the Honey Bee, where they'll execute him. Orthe player can set up a trap for the guards and extract him. The main reward at stake here is the location of the hidden mission objective, getting a most likely good soldier and completing another hidden extra objective. Certainly a pretty good reward in it's own right since the caverns are big and double back a lot. Seems like a wash design wise since both offer a lot to do with the prisoner.
So what about exploring? As pointed out, both areas in the games offer substantial shortcuts if you explore. Both offer rewards in terms of hidden items. Diamonds and materials found are arguably more valuable due to the improved economy over 4, which basically gives infinite drebin points. But MGS4 does give out that shotgun and chaff grenades, unique items that can't be found elsewhere. The rest of the guns are basically worthless though, and MGS5 has similar things with blueprints or prisoners that can make new guns, but not in this mission. So it seems about the same to me.
So then there's the boss encounters, vs. Skulls and Laughing Octopus, respectively. First time through, Octopus is definitely more substantial, with all her tricks and such. And the Frogs offer a nice chance to potentially sneak up on them for a change rather than just shooting, the only place with really varied tactics possible in the fight. I have to give the gimmicks and bombast to Octopus certainly, hiding as a dead enemy or a painting, its great! But I really like the encounter with the skulls too. Because it has the one thing the actual fight with Octopus is lacking, a myriad of ways to take her down. With the Skulls the player is given an immediate choice, use the honey bee or not. If used it will mean be throwing away a lot of mission points. But if one doesn't care about rank it's got a great weapon to use. Miller also makes it clear running is a viable and safe tactic and that meaning the potential is there to run or sneak past the skulls. On top of that there's even more options, not spelled out explicitly. Such as the way I went my first time through, my plan was to try using an LMG but that fell through and I figured the fight out in a different way:
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Nah Bloodborne was straight. Can't really think of any major issues. I'd say best game of the year so far.
I tend to get real ugly with games I like a lot let me down in certain aspects. You should've seen me around the time Uncharted 3 launched. 
Boy was I harsh on UC3 even though I played it like crazy.
That game was complete trash. The other games were so much better. 
