NBA 2k6's visuals will amaze you if you have an HDTV, but is still a great game of basketball that plays extremely well.
Whether HD or not, this is still a good basketball sim. Skills we be rewarded but if you are careless (aka chucking a pass three-quarters down court), or even making one too many passes on the fast break, you will get picked off. The only complaint about gameplay is that with a good shoot (cough Kyle Korver cough) you can step a few steps behind the arc and drain 3's all day.
Sound. Up and down. Crowd is loud and announcers are OK, but some noises like dunking sounds, just don't seem right and are just like NBA 2K5 on Xbox.
You'll have a good time with fanchise if you buy it, or it's fun for a week if you rent it. (seeing as acheivement points can be easily well...acheived with the sliders or a created player).
HD- Worth playing...definately
SD-If you don't care about the reduced graphics...worth playing.