Shadow Complex is one of the best XBLA games to come out yet
Shadow Complex is awesome. If you've ever played a Metroid game, you should know what playing Chair Entertainment's creation is like. The gameplay focuses on exploring a huge complex and upgrading your character to unlock new areas. The constant sense and desire of progression, along with a pretty solid shooting engine make this game pretty addictive.

The real goal is to explore the gigantic complex, level up and find upgrades. You always have a blue line that points out the way to the objective at hand, but the game encourages you to stray of the beaten path to find upgrades. And there's a serious amount of upgrading in Shadow Complex. Jason starts out with a flashlight and the ability to jump and crouch. However, by the time you finish the game, you'll have some pretty crazy stuff, like a helmet that's completely bullet-proof (when you are moving slowly), rocket boots to triple-jump with and a gun that shoots foam upon which you can stand. As you are going around, you'll find plenty of new toys that will then allow you to reach previously inaccesible areas in the underground facility. Besides new weapons and equipment, you can find upgrades for your maximum capacity of various items (e.g. grenades, missiles, foam rounds) and health. Exploring and killing enemies levels you up, which also earns you stat boosts.
Apart from running around to improve your dude, you'll also fight many a foe. Jason finds a simple pistol early on, but he'll find increasingly advanced guns over the course of the game that come equipped with unlimited ammo, a laser sight and a built-in flashlight. Other than that, you can also blow up enemies with grenades or missiles, or you can opt to freeze them with some foam. Cover is very important, as is positioning. If you don't stay crouched behind the game's various slabs of cover, and try to get height advantages, you tend to die rather often. At least, in the beginning of the game, when you don't have enough weaponry on your body to invade a small country.

The aiming happens with the right stick, which works quite well. However, while Shadow Complex plays in 2D for the most part, there is plenty of shooting over different planes. Even though you can see where you're aiming thanks to the laser sight, shooting can feel a bit clunky in those moments. Still, coming to grips with the game's aiming mechanics is pretty easy and intuitive.
If you feel like getting up close 'n personal with the Restoration's grunts, you can melee enemies, which simply requires you to run up to them and witness some pretty awesome Matrix-like animations in which Jason beats down the enemy rather brutally. Once every so often, you come across a turret, and using it flips the perspective and turns Shadow Complex momentarily into a 3D game. They're a nice change of pace that's sprinkled throughout the game.
The singleplayer game in Shadow Complex is definitely not bare-bones, but there also is a series of challenges present that you must complete as quickly as possible for achievements and leaderboard rankings. These challenges start out pretty simple, but get quite hard later on, and they do a good job teaching a player the various uses of the game's items, like the hookshot and Foam Gun. Leaderboards are a pretty big part of Shadow Complex, because lots of stuff is being tracked. There are achievements for doing X a set number of times (i.e. melee five dudes) but after you gain said achievement, the game keeps tracking the amount of times you've done X and matching you against your friends, which is great. Trying to overtake my friend in number of Bomba's punted was quite addictive, and even became exhilarating when my friend was playing at the same time as me. Trying to punt more Bomba's than him in real-time kept me entertained for quite a while.

Shadow Complex looks fantastic. During cutscenes, its arcade roots are noticable, but when Jason is simply running through the complex, it's not too hard to mistake it for a retail game. The complex's hallways look bland, as any sterile facility intended for evil goals should, and the animations are good too. The music is always in the background, but when it does show up in the soundscape, it does a good job highlighting an important moment. For an arcade game, the presentation is just unreal (pun totally intended.)
Shadow Complex clocks in at around 5 hours first time through, but I was easily enticed into starting a second run to find all items and continue leveling up. There's easily enough content here to justify the 1200 MSP this game will set you back. And I highly recommend you to spend that money on this game. I assure you that you won't regret it. Buy Shadow Complex. Now.