Got NHL 2K8, didn't really need a demo for it (gameplay we knew was much like 2K7 just tightened up a good deal) as there was a full game online I could watch. A 5 minute demo can hide a lot, a full game shows you everything.
Anyway 2K8 is a nice improvement over last year, the controls take a while to get used to, one-timers are much harder to score on, the goalies are much improved and the graphics you all have seen. Kopi has the tinted visor and Brownie is dead-on, as is the Kings light show at the beginning of the game which really gets a Kings fan pumped to play. The Kings have their actual equipment and you can change any of it if it's not to your liking. JMFJ (82 overall) , Nagy, Handzus, Calder, Stuart, are all there, probably have to get Klemm to make my Kings team complete before I explore Franchise mode, I like to have ALL of our Kings on the team.
A lot of people are getting turned off by the new control scheme and menu but feel free to go back to the classic control setup and you can find the sliders under My NHL-game-styles-View/Edit.
It's nice to see the AI play well in the neutral zone, and it really makes it tough to hold onto the puck for long. Each team has it's own playstyles and certain players even have their own styles, all of which you can edit.
Haven't played a ton, but it certainly is an improvement over last year, especially once you get past the new controls, but there's a training section which shows you how to do them all and then practice as long as you want.
The superstar moves are fun if you can get them down (all can be learned in training mode, use Kopi or Fro to pull them off), and once you kick the puck up, flip it up into the air, and bat it into the net and Staples Center erupts it is very rewarding. Enjoying the soundtrack too, Quiet Riot's "Come on Feel the Noise" is a nice one to hear after a sweet goal.
Just some thoughts I had after a couple quick games, hope they help out some, don't listen to the reviews of people who spent an hour with the game and gave up, I am one of those who loves a challenge.
The Skybox is toned down a lot this year, you still can unlock 82 and 93 Kings teams but to do so you have to play the Sharks and Canadiens and beat them to get the Kings unlocked for those years.
The intensity is still there from last year, or chippiness is a better word.

If you come out and play a soft game, that's fine the AI will do the same, but if you start running their top players, they will start hitting back and running your guys. Then it's time to throw Raitis on the ice and he will settle things down for us with the improved fighting. You can duck and bob and weave, even get good enough to come out of a fight unscathed if you get the rhythm down. I never liked 2K's fighting before but this year it's better. Incidentally so is the checking, big guys have an easier time taking out smaller ones, and they can't do it all the time, and on one exceptionally good hit I got the Dodge Nitro Hit of the game.
In 2k7 if you pressed the line change button you would sometimes miss a replay, now it does the replay and then lets you select your lines, and there's even an option for the 5 second NHL rule to set your line changes.
Perhaps one of the best things in 2K8 is faceoffs now, it actually takes some work to not get thrown out of the faceoff circle now (if you are aggressive like I can be), and some strategy, have another faceoff guy ready to come in if your starting center gets tossed out.
Hope that helps, sorry it can't be more but I am just getting the hang of it and haven't even gone into franchise mode yet.