I'm not quite finished with the game yet but I have logged in plenty of hours already. The graphics are some of the best yet. The characters all look great, the guns look awesome and the environments look amazing.
The AI is improved from previous games and it makes it a bit more challenging. One complaint I would have with this is that they can detect you a lot quicker even when you're disguised. It makes it a lot harder especially on the smaller maps. That brings me to the map size; some of them are huge and some are small and compact. In the old Hitman games I really liked bigger maps with more freedom and it seems like they got away from that. Regardless, that's just my opinion and there is still a lot of freedom in the game.
The new point system is great. It makes it much more competitive with friends and always makes you strive to get the best score possible. I've repeated checkpoints countless times to try different approaches and techniques. I have yet to get deep in to Contracts mode but from what I've played and seen it can be just as fun and more competitive than the campaign.
The story is really the only downfall so far. I have a hard time wanting to follow through most of the cut scenes but that's mainly because I just want to play the next mission, it's that addicting.
Definitely rent this game and give it a try! As for you hardcore Hitman fans, you'll probably keep this for awhile. There is a lot of replay value for this game and it's always fun to 1-up your friends' scores in Campaign and Contracts mode!