I've played 4 games against the CPU AI, on superstar, 3 online games against a buddy, and spent hours in the freestyle mode of 2ku. Here are my impressions after maybe around 8 hours of gameplay in 2k18, and a week of playing the prelude.
1. The controls this year are the most fluid and responsive they've ever been. It's great that this year they've finally been able to chain all the jab steps, pivots, escape dribbles, and dribble moves off the triple threat/post with excellent fluidity. It's really fun to use elite ball handlers and scorers in triple threat positions to chain together some great moves and replicate some signature combinations in real life.
2. The 5 on 5 gameplay is really good, with both the CPU opponent AI and your own teammate AI being really intelligent in terms of reading situations and reacting. There's one thing I'm noticing on defense though and it's the tendency of 'overhelping' to the point where some players are left wide open (like not even a few feet away from them) in order to pre-help. To counter this, I adjusted the off-ball defense settings manually. Also, one thing I noticed was that the CPU has a tendency to force alleyoops sometimes, leading to some bad turnovers. One other nitpick is how strong a lot of the set actions are, particularly when people get stuck behind multiple screens, this leaves a lot of players wide open for a long time when you fail to chase them down screens - it leaves a lot of work for you to try to manually control just to make sure that you get to the offensive player on time. Other than that, I'm happy with the gameplay, minor clipping issues aside.
3. In my 4 games, I've played the classic kings vs the 01 lakers (sucks that the kings are only 8 deep, with Hedo being a big loss for the team), and 3 games as the nuggets against Boston, OKC, and Houston. Each team played a lot like themselves, particularly Houston, which shot something like close to 30 3s, and was relentless attacking the paint. The pace of the teams feel different (with OKC trying to slow things down) and Boston doing a lot of Brad Stevens sets, with some Iso mixed in for Kyrie. Feels great.
Anyway, game is great. Online so far held up for me (with no input lag) through 3 games that i played yesterday. I'm sure as I get used to the new mechanics, and the new systems that the shine on the game will wear off (and as the community learns what to abuse lol), but this has been great, they've addressed a number of legacy issues in this game.