The greatest ever? Revolutionary? No, but a solid, stylish game with more meat and depth than the vast majority of FPSs.
Here's a breakdown of the positives as I see them:
1) Sound, effects and voiceovers. Picking up diary tapes helps to round out the story and describe what happened in the past, before everything became a disaster. Splicers can be heard talking to themselves, and have a decent amount of dialogue, enough so that it doesn't become mind-numbingly repetitive half an hour into the game. The sounds of the city itself are fine, but the weapons lack punch. 2) Character development and skill progression. Special powers (plasmids, think magic) and physical, weapon, and engineering tonics can be used to upgrade the character, allowing him to freeze, shock, or burn opponents, use telekinesis, create decoys, run faster, turn invisible, or hack more efficiently, just to name a few. There's also a camera which allows you to take pictures of enemies to earn bonuses against them or gain unique abilities. Weapons can also be upgraded.
3) Graphics. It's a mixed bag, honestly. At higher resolutions, some of the textures look really muddy up close. They look more like textures you'd see on the 360, and that's almost surely what they are. The water is extremely well done, however, and luckily there's lots of it, lots of ripples and reflections. The character models overall are decent, ranging from the impressive Big Daddy that shakes the ground as it walks, to the less impressive array of splicers who look less detailed and distinctive.
4) Animations. Everything looks fluid and lifelike. Absolutely no complaints in this department.
5) AI. Surprisingly good AI which doesn't break very often. When it does, it's usually due to a path being blocked. Enemies act much more unpredictably in this game than almost any other I've seen. They can dodge, charge, take cover while reloading, or run away and heal themselves at a med station when badly injured. Some of them, namely the spider splicers, can perform impressive acrobatics, doing back-flips and crawling on the ceiling. You'll never see an enemy standing in the same place for more than a second. They're always active. Even in non-combat situations, the AI is always on the move, interacting with the environment, searching corpses, using the vending machines, etc.
6) Environment interactivity. Most objects can be picked up and thrown via telekinesis. Oil slicks can be set on fire and water can be hit with electricity, shocking anyone standing in it. You can set a corpse on fire and throw it at an enemy, as an example. I guess hacking could be considered part of the interactivity, which adds another dimension to the game. The hacking minigame is identical to that of Anachronox. 7) Physics. Due to Havok and UE3.
The negatives:
1) Serious lack of variety in enemies. When you remove Big Daddy and bots from the list, all you have left are splicers, and they are all interchangeable, other than the weapon they carry, either a machinegun, pipe, box of grenades, or a pair of hooks. The Houdini splicers are the magic-users of the group and while they have some interesting abilities they still look pretty much the same as everyone else - grungy humans with malformed faces. They fit the story alright, but it would have been nice to see some other creatures thrown in, perhaps more mutated and extreme versions of the splicers. The Little Sisters all look like clones, only with different hair and dress colors. While everything else looks fairly realistic, they look more like anime characters than real girls.
2) Excessive enemy spawn. Kill a bunch of splicers in an area, come back 2 minutes later and there's a whole new batch.
3) Smallish levels. On most maps it's possible to go from one end to the other in less than a minute (assuming a straight run and no fighting along the way). This is likely due to the limited memory of the 360.
4) Simplification of gameplay. SS2 had more complexity, sometimes to a fault, especially when it came to weapon breakage. Some may like things 'streamlined', but I prefer a little more depth. It has to work for the console, so not surprising.
5) The ending. No spoilers, but it was too cliche for a game like this. And it was laughably easy to boot (on hard, with no Gatherer Garden upgrades bought). More disappointing the more I think about it.
6) I didn't like the instant resurrection of the Vita-chambers. It kills the challenge and interrupts the flow of the game. Not a big deal really. Just reload if you 'die'.
7) Neither scary nor suspenseful. I don't know if this was one of their goals, but it didn't happen for me.
8) No replay value. No multiplayer. I was able to get both endings by only harvesting/rescuing at the very end. The game was remarkably stable on my machine - not one crash. After an extended period of time (6 hours continuous), the game started to get a bit jerky (pausing occasionally for less than a second) as it appeared to be running out of memory and dipping