If you played 2k7, that's what 2k8 is. People nicknamed it NBA 2k7.5, because they really didn't change anything except update the roster, add a few more shoes. Graphics are the exact same. Commentary still sucks. No 24/7 mode, no blacktop dunk contest or 3pt shootout, no additions to association mode. I already have 2k7 for PS2 and I don't even play that, so I'm definitely not getting 2k8. It's only good for 360/PS3, because on PS2, hardly anything changed from 2k7. So if you have/played 2k7, that's pretty much what 2k8 is. But since you haven't played since 2k6, I guess it would be ok to get 2k8, but the 2k series is best on 360/PS3 either way. I really gotta upgrade from a PS2.
I got 2k8 for PS2 and to be honest I probably shouldn't have. Not because it's a bad game cuz it's really great, but because like Richie said it's almost literally the EXACT SAME GAME as 2k7. I'm getting a PS3 for Christmas so i probably should have just played 2k7 til then, but if the last game you have is 2k6 then yeah it probably wouldn't hurt to grab 2k8. It's only like $30 anyway