Fate/Zero is

. I watched it when it first dropped and haven't seen a better anime since. Some of the best animation I've seen in something that's not a movie or OVA. Might be a bit confusing to those who don't know the series' back story.
Fate/Zero is the prequel to the Fate/Stay Night series. It can be confusing cuz the Fate/Stay Night series is based on a visual novel game that has 3 routes you can take based on your choices. The routes are Fate, Unlimited Blade Works, and Heaven's Feel. The anime is mostly the Fate route, but takes parts from the other 2. Fate/Zero was a light novel that came after the game. There was also a movie released about a couple years ago that was based on the Unlimted Blade Works route.
The Fate/Stay Night anime is sh1t IMO, but it does animate one dope fight that happens off screen in the game. Hopefully the remake is better. It would be cool to see them do a Heaven's Feel route since it's the only one that has a dark enough tone to match Fate/Zero's. Some of the sh1t that happens in that route

.
It will always be Fate/Zero > Fate/Stay Night to me cuz the characters and story lines are better. Movie was dope too, but feels rushed since it tries to fit the whole route into that one movie.