People usually say that Nas is terrible at selecting dope beats but the real problem has always been his hook game. When a beat is just average, it doesn't really matter much if you create a good hook and write a good song. If you're a good songwriter, you can turn a very average beat into a great song.
The problem is Nas' hooks have often been very simple or amateurish. Even on Illmatic, most of the hooks were just repeating the name of the song. Obviously, on Illmatic that doesn't bother anyone and it works well for that album.
However, on his later albums Nas has been really hit and miss. Nas is one of the best pure spitters of all time easily but he's not quite a natural songwriter like Pac, Scarface etc. I think they are better songwriters overall though when Nas does stay focused he obviously writes some of the best songs in hip hop too. The reason for that is just the way he writes his lyrics. Nas often jumps from topic to topic in a single verse without necessarily sticking to one theme. It's like he doesn't really know where he's gonna go with his verse and just tries to follow up one dope image with another, even if they are not necessarily related. You kind of have to read the coherence into the songs which can be quite a fun exercise but which can be annoying when there seems to be very little (which is basically what Jay accused Nas of doing on Takeover and Blueprint 2).
It's a problem that happens to a lot of people who are more lyrical, their content kind of switches up more because the content follows the rhymes. That's why rappers with simpler rhymes like Ice-T, Ice Cube, Slick Rick, Easy-E etc. are able to write more straightforward songs and stick to the same topic. Nas takes more of an approach of conjuring up some sort of imagery which is more poetic but also less focused usually.
That's why he has trouble writing hooks that describe what the song is about unless he's doing conceptual songs which are usually his most revered songs.
The Lost Tapes and Life Is Good are as good and popular as they are because Nas' songwriting abilities seem more focused and the hooks are more on point.
Anyway, that's my 2 cents.