Aliens: Infestation is best described as Metroid set in the Aliens universe - replace Metroid characters with Aliens while retaining the 2D map and exploration experience, and most of the time that description is fairly accurate.
Unfortunately, it tries to add its own little differences, some of which are executed better than others.
You control one - from a squad of four - marine at any one time. There are 16 more marines to enlist when you have a free slot (i.e. someone dies), and I managed to lose nine on my initial play through. If one marine dies in battle, you need only find one of the replacements spread throughout the space station. All of the marines share the same abilities making them little more than extra lives.
You manoeuvre these marines through the USS Sulaco, a broken down cargo ship occupied by xenomorphs and the staff of an unnamed company.
Aliens: Infestation's story goes that some scientists working for an unnamed company have developed a new breed of xenomorph - a hybrid of the alien species and chimps. The plot is laid out through dialogue segments between your current squad member and the commander.
Although the dialogue changes slightly between marines, it always has the same result: "go there and grab this or kill that thing." Likewise, there's dialogue when encountering a new marine or the final boss.
Although it's a nice touch, there is a bit too much dialogue, and it makes reading the cut-scenes an unwanted interruption when you are joyfully killing xenomorphs.
Aliens: Infestation doesn't hold back on diversity of its enemies, with various guard robots, humans, and a variety of xenomorphs to shoot/blow up. As you progress the enemies switch from slow robots to more agile xenomorphs.
Guard robots appear early and are much easier to kill because they can't fire downwards, and one or two grenades rolled in their direction will break them. If you don't have any grenades, Aliens: Infestation features a cover system; you can get behind a crate and shoot human or robot enemies with your side arm - however that tactic doesn't work on xenomorphs.
The xenomorphs aren't particularly hard to kill either; unless it's a boss battle one grenade is usually sufficient - and they usually appear one at a time. However the xenomophs are a lot quicker than previous enemies, so your practiced tactics won't work and the cover system is rendered pointless.
In rare cases you'll have to fight multiple face-huggers - fortunately they do minimal damage and you can take a dozen out with a single grenade.
Aliens: Infestation's map is its best feature and, when equipped with the radar, can also help you kill the xenomorphs more efficiently. Not only does it display the main corridors, it also marks the position of every character in the current room - allowing you to predict the where they will show up and lay traps or throw grenades accordingly.
Unfortunately, the map isn't complete. While it does show all of the main corridors, Aliens: Infestation features many hidden areas where most of the key items and power ups are hidden.
The marine's arsenal is pretty good for a 2D shooter. You have two automatics, a shotgun, a flame thrower, and a pistol as your sidearm. You start out with a machine gun which can fire explosive shells and the side arm, collecting bigger guns as you progress. The flame thrower is the most useful of the guns you'll pick up as it doesn't just burn things to death, it also acts are one of your tools - burning the sludge off previously inaccessible doors.
Each gun can be upgraded a few times via upgrade boxes. Unfortunately, upgrading can be a huge inconvenience as the upgrades will only be applied to the gun in hand. So If you come across one and your gun is fully upgraded you'll have to find a communications center and switch to another gun, then go back to the upgrade box.
Players will also get to pilot a the power loaders - those "wearable forklift" things made so memorable in Aliens itself. Although they are just as unwieldy in this Aliens: Infestation as they were in the movies and relegated to crate smashing, they do a good job of protecting the player. It feels like the blocks are there simply as an excuse to include power loaders. Fortunately, the segments using the power loaders are kept short.
As you progress you'll collect tools required to open up rooms, including a welder for unlocking doors, and various key cards for accessing lifts. At one point you steal a key card from a naked man's towel (this doesn't say much for the marines' morals does it?).
Other useful items include the flares, which can be used to mark key locations on your radar - like a weapon upgrade or marine you'll be able to pick up later.
Unfortunately, not all of the new things Aliens: Infestation brings to the table are well executed. For instance, there's a short chase sequence in which you escape in a tank while fighting off xenomorphs. The gun is controlled via the touch screen, however the control method is poorly implemented and at the end of the run your tank crashes so you're left wondering why you even bothered shooting at all.
In another, there's a spacewalk segment in which you're trying to jump between platforms in low gravity. This segment is full of leaps of faith and will often lead to accidental deaths. The only redeeming feature of this section is the decent space pistol which can take out the xenomorphs outside with a couple of shots.
Another design oddity - while not really a problem for the player - is that before you get to the final boss there's a communications station. In the next room, there are health and ammo packs. The packs are rendered pointless due to two things: first, communications stations replenishes both to full. Second, the door to the room with the health and ammo is locked once you enter the boss room.
Beyond the odd design decisions there were numerous sound glitches such as weapons fire effects echoing in certain areas. In addition, the game crashes during the final boss battle in a supply room above the boss room - how it's triggered isn't clear, but it happened twice.
This title isn't very reseller friendly either, as once you've unlocked everything, you can't delete the unlocked data - such as marine bios and credits. You can erase the saved game, but anything you've unlocked will remain. The bios of fallen soldiers will revert to their 'alive' status in the new game.
Overall, Aliens: Infestation is a fairly enjoyable title that's let down by a few glitches and questionable design decisions. The best things it has going for it is the budget price (around $60) and that the majority of the game is the classic Metroid-style exploration.