This game seems like a standard third-person cover shoot inspired by Gears of War, but the ability to mess about with gravity adds loads of extra fun to the game. Also the story and characters seem pretty generic and uninteresting at first but as the game progresses tensions develop between the main characters, and the plot becomes more interesting as there is mystery as to where the invaders come from and why they are really here. The story has a pretty amazing twist which does actually have clues earlier in the story but you are unlikely to guess in advance!
The graphics are excellent and there are decent menu options that allow you to configure the settings according to the power of your PC. Also if you have a 3D monitor or a 3D TV this game is a must-buy as it looks amazing in 3D, the game has been fully made for 3D and even the cutscenes have perfect depth. Note that you do not need to have a 3D screen to fully appreicate this game, even in 2D it looks great, but if you do have a 3D screen then it adds an extra level of awesomeness. The game has loads of bits where debris and objects and body parts and blood are floating about in zero gravity and it looks amazing walking/floating through all the floating stuff in 3D. Metro 2033 is similar, the amount of dust floating everywhere makes 3D an impressive experience.
The multiplayer is excellent fun. Normally in games like this the person who camps somewhere with a sniper rifle will win the day, but in this game you can use your low gravity power to make him float out of cover and be vulnerable. I like to then run up to them and do a melee instant-kill finishing move such as slamming them into the ground and stamping on their head. But because this game is not very popular there are not many people playing multiplayer; sometimes you can get good games with 8 people but at other times you end up with just 2 or 3 people in a match; your best option is to join the Inversion steam community group and that way organise a game with other Inversion players.
I did not have any trouble changing the controls. Most PC games nowadays have your "aim" button bound to the right mouse button, but by default Inversion binds your "aim" button to the E key and instead puts your gravity powers on the right mouse button. This is not a terribly new situation, I remember both FEAR and FEAR 2 had your right mouse button being your melee attack key and the zoom/aim button was the SHIFT key. I think Sin Episodes: Emergence had the zoom key being the Z key. Anyway, you CAN change this if you want, you can make the right mouse button be your aim key if you want. Though apparently a few players have had a bug which prevented this from working, but on the Steam forums most players have reported being able to bind actions to the mouse keys without a problem. Personally I found I did not need to modify the controls, after just a couple of minutes I got used to pressing the E key to aim my gun and using the right mouse button to fire my gravity powers.