Team 17, the people behind Worms, originally scared kids all around the world with Alien Breed back in 1991. A classic Amiga title, Alien Breed set players the task of surviving in a post-apocalyptic environment where the Aliens are very much in control and everyone else is dead.
Evolution Episode 1 doesn't stray far from the original - you start off in a space ship which has been overrun by an incursion force of StarCraft Zerg-like alien nasties which have an annoying habit of bursting out of the floor behind you.
The camera has been moved from the Gauntlet-like top-down variety (found in the original) to an isometric camera, giving you some angle on the well-detailed environment. Loads of physics-enabled garbage, fire and nasties fill the Unreal 3 engine-powered world, giving the game a retail feel - it punches well above XBLA weight, especially given it's only 800 points. You can control the camera by tapping LS or RS to nudge it 45 degrees in either direction. It's handy but a little bit awkward to be doing too often, given what your fingers will otherwise be doing.
Your little marine dude is controlled with the left stick, while the right stick controls where he's aiming. You need to press the right trigger to fire your weapon, while the left trigger uses whatever item you currently have selected. You can change the selected item (or weapon) by using the d-pad; up and down changes items while left and right switches weapons. Your basic weapon has unlimited ammo but it's not very effective against anything, so you need to keep a constant eye out for extra ammo littered around the levels (often on the corpses of those that came before you).
Aiming works well, with a little targeting laser helping you hone in on the alien hordes. A little bit of soft-locking wouldn't have gone amiss, as wasting ammo on shots that don't make the target is a little frustrating - especially on the higher difficulty settings. The enemies can also be a trifle difficult to make out - adjusting the gamma levels helps but little health bars over the heads of enemies would have helped out a lot more. There is a scanner which shows the location of enemies in relation to you but, true to form, it too is difficult to see much of the time.
The core gameplay involves traversing the levels, finding keycards and generally trying to progress by performing various mini quests that are unveiled as you solve the previous problem. Along the way aliens will assault you, keeping you on your toes. Smart use of your environment will help to keep you alive, as will the weapons you get along the way. Each has it's own strengths and weaknesses, with the awesome looking (and incredibly powerful) flamethrower being a highlight. None of the weapons is particularly innovative or exciting but they fit the setting well enough. Combat is similarly pretty much exactly what you'd expect, with no combos or skill-based bonuses to spice things up.
There are five levels in the first episode, with a couple of extra multiplayer-only levels to play in. Each level takes a decent amount of time to find your way around, resulting in around 4-5 hours of play for your first run-through. Multiplayer feels different, with less of a "quest and explore" feel and more of a "ohgodaliensrunaaargh" manic survival horror feel.
All in all, it works pretty well - it looks nice, is fun to play and has an awesome "Crusader: No Remorse" kind of feel to it, something no game in recent memory has managed. It is to the top-down action / horror genre what Shadow Complex was for the side-scrolling version of the same. It's not perfect but it's definitely well worth you checking out - with a few minor tweaks, Episode 2 could be a serious downloadable game of the year contender!