After spending the better part of two weeks playing NHL 2k9, I just shipped a review of it off to Bill, which I'm sure he'll link once it's posted.
It'd be easy, on first impression, to write this game off in the face of EA's NHL 09. There's not much flash to it. But it plays a very, very solid game of hockey and I'm at a loss to explain the 70 Metacritic composite score it's getting.
I read a few of the reviews and either I'm crazy or some of these guys are, because we're clearly not playing the same game. There are criticisms of the AI over-pursuing the puck like crazy and of goal scoring being way too easy that, once I bumped the game up to the All-Star level, just didn't seem to be the case. I'm not saying it's perfect, but I think it's way better than these composite review scores suggest. In fact, if you can get an open slapshot in front of the goal on All-Star you must be better than I am (probably not saying much) because I could hardly draw the stick back in prime scoring position without getting plowed or pick-pocketed by somebody. (Also, with some slider adjustments, your mileage will vary too.)
Also, nobody seems to mention the puck physics in the game, which I think is a huge perk. EA's game has good puck physics too, but 2k's is a cut above, IMO.
The only truly killer grievance I've got with the game is with the Franchise Mode, where too many all-star caliber players go unsigned. That is just a horrible, horrible oversight. (Season to season stats are also low, in terms of scoring, but not egregiously so.)
I can't say this game is better than NHL 08/09, but that's not because I think EA has a smarter hockey game. There's just something about the EA NHL series right now that, for me, makes it more fun to play. It's got a panache to it that 2k lacks. But that said, if your sole criteria is getting an authentic, challenging hockey game, you should give NHL 2k9 a serious look. Just don't play on Pro (where it is way too easy to score because the defense is horribly lacking) and check the Operation Sports forums for a decent set of gameplay sliders. (I don't have the patience for working up my own set of sliders.)