Dark Arena was the first FPS to be announced for the Game Boy Advance, but it wasn't even close to being the first one released. And while its level of quality is comparable to that of its contemporaries, it's by no means the novelty it was when prior to its release. The game's sprite-based engine (think Doom and Wolfenstein 3D) facilitates the sort of gameplay you've come to associate with classic PC shooters, and if you haven't already experienced it on the handheld, seeing it happen on your GBA screen is pretty neat. If you've never played this sort of game and you're used to more modern stuff, prepare for a scaled-back experience--since the game's engine is essentially tricking you into thinking it's rendering everything in 3D, you aren't going to be able to move like you do in games such as GoldenEye and Halo. Your aim rests on a fixed axis, so you can essentially shoot things only directly in front of you. The actual mission design is similarly scaled back; it all revolves around running, shooting, and unlocking doors with their respective keys. It's all very simple, and you can argue that this is suited to the platform. But with all the complex stuff being released for the GBA these days, it's becoming a little harder to swallow.
If Dark Arena sounds like it's a Doom clone, it's because it essentially is. The visual design is fairly different, but the graphical style is largely the same. Imps and cacodemons have been replaced with mutant killers and mechanized attack bots, but largely, everything you'll do will ring eerily familiar if you've played any of id's classic shooters, if only half as inspired. The weapons you'll use are largely based on FPS archetypes as well; you'll start of with a handgun, and you'll soon pick up shotguns, miniguns, plasma rifles, and rocket launchers. Some are a bit more inspired, though, like the guided missile, which lets you traverse the corridors through a missile's eye view, and the energy cannon, which shoots forth a high-powered blast with a huge damage radius but requires a few seconds to "charge" between shots. Most of the weapons have very satisfying effects, though, and they're all animated quite well. The plasma blaster gyrates in a very cool manner when it's being fired, and the minigun's chambers spin quite convincingly. The game also has something of an auto-aim feature implemented, which lets you shoot at enemies in most parts of the z-axis. This helps quite a bit, but it doesn't always seem to work as intended; you'll often have to coax it into aiming in the direction of a particular enemy.
The game's weakest point is easily its enemy AI. Often, you'll be warped into a room full of enemies standing still, with their backs turned to you. Only after firing a shot will they react to your presence. It's a bit understandable, given the hardware constraints present, but seeing other games with much tighter AI--like the GBA Doom port--makes it a little harder to swallow. There are also a couple of instances of collision funk in some of the stages, which make it much harder than it should be to get around certain waist-level world geometry. These instances were fairly isolated, admittedly, but their occurrences were annoying no less.
In all, Dark Arena probably plays just like you'd imagine it to. But the fact that Doom has already been released on the GBA makes Dark Arena a much harder sell. It's technically competent in the end, and many of its little touches are quite impressive, but there are clearly more memorable shooters of its kind already available. The four-player deathmatch mode might warrant a look if you're already bored of Doom's, but otherwise, you're probably already covered.