I got the game a few days ago (ordered it from a UK store because it's WAAAAAY cheaper over there, 45€,60$ instead of 70€,100$, they sent me a Korean copy which was o_O but worked well anyway) and it's a ton of fun. Reviews are mixed and I can imagine it getting somewhat repetitive depending on how you play. Yahtzee's criticisms of the combat are spot on, most of the other attack powers are only of limited use, in part because switching is just so uncomfortable (you have to use the right analog stick) so you're going to stick with one and the extend-o tentacle just seems to be the most versatile one... Of course that doesn't stop you from using the others just for fun (and sometimes they're better at some tasks as well, the tentacle is just the best allrounder), just like you can use dropped weapons for some fun or actually bother with maintaining stealth instead of simply slaughtering everyone that comes along. The game certainly lets you take many different approaches to situations and manages to make stealth actually fun (in part because the stealth attack tells you when someone is looking and refuses to trigger instead of blowing your cover because you didn't notice that one guard waaaay over there). It's a bit strange how slowly climbing up a wall raises suspicion quickly while just hitting dash and running up doesn't bother anyone at all but generally the guards seem a bit thick when it comes to realizing who you are...
Anyway, it's one of those zero-consequence open world games where you can just pull any nonsense you feel like, whether performing cannonballs into crowds of onlookers or stealth killing an entire army base's staff one by one (BTW, you don't get the EP bonus for doing that so once there's only one guard left make sure to blow your cover and use regular combat).
I like the alert system too since it actually tells you when people see you and when your suspicion rating is going up instead of slapping a wanted star on you when it's way too late.
What stood out the most for me though was the unnecessary level of violence. You can cut people in half horizontally or vertically with very graphic results but it seems like gore for gore's sake, the game certainly isn't consistent when it comes to hit effects, while people just get ripped apart anything with more hitpoints causes the usual videogame effects that are only missing a text like "crack!" and "pow!" to look entirely cartoony. Big enemies just ragdoll and fall to the ground, no matter how massive an explosion killed them so I really don't get why they had to add elaborate gibbing mechanisms to the humans and drive the rating of the game up that way. While Prototype was strangely available from Amazon here it didn't show up in stores and got a rating refused so it's definitely hurting its marketability with that unnecessary violence (of course the whole consume and kill mission stuff may also have been enough to trigger that). Especially with the way the blood sprite looks just plain cartoony... Anyway, it's enough fun that they could have replaced the bystanders with puppies or kittens and it wouldn't have hurt it in any way.
The graphics look pretty meh in many parts, strange specularity on people and the blocky buildings of modern cities don't help much, the pre-rendered parts have pretty ugly hair and lighting effects too. The large number of people onscreen at least justifies the platform choice but some of these things could've been improved without a performance hit... At points I was missing Red Faction's building destruction but that was mostly in a tank...
Overall it's great fun that lets you do whatever you feel like.