I haven't gotten very far in any of these games, so this is more a "first impressions" post. Darksiders I'm barely past the tutorial type areas into the meat of the game, Dead Island I think I'm still in Act 1, and I'm the farthest in Deus Ex having just killed the second boss.
Darksiders - This game is just plain fun. It's a Zelda game minus Princess Zelda and set in hell (well, hell on Earth, but still). The combat is pretty basic but I still had fun with my button mashing. Plus in order to beat some of the bigger baddies you have to time your button mashing with jumps and figure out where they're weak, so it still poses a challenge. The only downside of this game so far is that you can't play it with mouse and keyboard. Don't bother trying to refute that. If you are playing this game on mouse and keyboard you are doing it wrong. Go buy a USB game pad. The controls are very good, so even if you're not use to a game pad you shouldn't have issues.
Dead Island - I'm back and forth about this one. It's a fun game but I'm finding myself getting hung up on a lot of the details/mechanics. The worst one for me is the weapon fatigue. It feels like you can use a weapon for maybe 10-20 hits on zombies before it breaks and you have to use a new one. Plus, as pointed out in Zero Punctuation's hilarious review, you can just kick a zombie to death and not have to bother with weapons at all. There is an ability that let's you one hit kill curb stomp a zombie once you've knocked it down with the first kick to its gut. For the thugs you can just toss molotovs at them and wait for them to burn to death. Despite this, I've still been using weapons (mostly because I am prone to lighting myself on fire with molotovs) and it's fun until they die and I'm left trying to kill things with a tiny splinter of wood. Overall it's not a very hard game though, especially if you go with the health regeneration tank character to distract things from your knife expert stabby in the back partner. And despite how other reviews I've seen have marked this as a negative, I think it's hilarious that most of the characters in the game-including yourself in a couple iterations-are mostly drug addicted drunken assholes. It's a nice change from the regular zombie apocalypse assumption that the majority of people who would survive would be nice people.
Deus Ex: Human Revolution - I have been having a lot of fun with this game! The story is pretty immersive and the characters are very well done. The combat is a hoot, especially since the game very clearly encourages you to sneak your way out of trouble but doesn't mind if you're a crazy person like me who says fuck sneaking and opens fire in a room full of guards. I like that there are multiple ways to get where you want to go and complete the various missions. Even though I've tended to take the exact same "shoot them in the head" approach to all my quests, I still appreciate the fact that I could have spared their lives or snuck in and hacked my way out of it.
Of course, that brings me to the major issue with the game that pretty much everyone who reviews it agrees on - the boss fights are stupid. Like, really stupid. In the entire rest of the game you have multiple choices and options, but for the boss fights you have to fight them in the one way the game tells you to fight them. Instead of having vents and back doors and multiple entrances, you're stuck in a small room with a boss that can break you in half in one hit and only one really dumb mechanic the game wants you to use to beat them. It's really, really disheartening to run into a boss fight after having a blast screwing around in the rest of the game and it does this game a great disservice. I think it's interesting too that most reviewers say something like "well I built a computer science sneaky dude for the rest of the game so that's why it's hard for the boss". That is extremely misleading since there is no other way to build your character! There are a billion options for stealth and hacking compared to a couple that might help you fly in guns blazing.
I would probably still recommend this game since I've had fun between boss fights, but whereas I might have recommended it to a non-gamer for a nice entry FPS on easy mode, I would no longer do that due to the idiotically out of scale boss encounters. For veteran FPSers though, it is worth picking up.