It's got the new rules, new rosters and...nothing else.
NHL 06 has some new features, such as the return of Create-A-Player. It has been enhanced, but is still not of the best quality. You can goof around with giving your hockey player broken noses and black eyes, and you can make him fat or skinny if you want too, but he's still gonna look all that great. Besides that, the game sticks to the tride and true formula they've had since NHL 94. Speaking fo which, NHL 94 has been included for free within the game, and it's a nice little feature to see how little the game has really changed. It's exactly the same as the original except the Hartford Whales were not included due to legal reasons. The graphics in 06 are solid; the characters move smoothly, but you won't really look and say "That bunch of polygons looks just like Todd Bertuzzi!" The sound get's the job done. Every game has commentary which ussualy consists of comments like "insert name has worked hard this game!" or "so and so makes the save!" Needless to say, it's not like the real thing. There's some good replay value with the multiplayer, but the single player won't really have anything to keep you coming back.
It may seem like I'm bashing NHL 06, but it's really not a bad game. It's just the same one we've been playing for years, and it's starting to tire. But it's wholely reccomendable to hockey enthusiasts, and a great rental to everyone else.