The difference between all the NBA2ks?

I currently only own one version, NBA 2k13 I purchased 2 years ago. See I'm wondering if it's even worth it to buy the new version every year. I went from NBA 2k13 to 2k16, and I felt like the menu interfaces were the same, the same game modes. There is this new 2k battle thing, but I wasn't quite digging the draft. I guess I notice new animations, how the players sprint, new commentary, etc. So basically the mechanics have changed a little that took some getting used to. But I just could not properly do an alley oop! I couldn't figure out how. The game itself is not bad, but I just didn't think it was significantly different enough.

Bottomline is, is it worth it? Also could you guys list the major improvements or differences for each subsequent 2k game? Thanks.