The Metal Slug series is one of those litmus tests for gamers. Some think it's the pinnacle of classic, 2D arcade side-scrollers such as Contra and the recently 360-fied Alien Hominid. Just two gun-toting friends charging constantly to the right, blasting every superdeformed tank, copter, soldier and ammo dump in your path into fireballs in an orgy of bombast and buddy-dom. Others call it a fossil, dislike 2D graphics no matter how great the animation, aren't moved by giant explosions or whimsical game design, and think these games are just too damn hard.
Metal Slug Anthology, which collects all seven arcade Metal Slug titles, is destined to reinforce both of those schools of thought. But given the choice, we'll take the one that lets us unload into projectile-vomiting zombies, drive jumping tanks, get fat, fight giant mutant barracuda and ride camels with laser cannons in their saddlebags.
The games themselves - Metal Slugs 1-6 and the 2.5 version called "X,"play smoothly with the PSP controls, and though they have to be blown up slightly to fill out the PSP's screen (there's a too-small authentic view and a too-stretched widescreen choice as well) it's some of the best 2D you're ever likely to see. Of course, they play beautifully but brutally, like the arcade-tuned, nerve-grinding, reflex shredders they are - you can set it up for infinite continues if you like, and even save your game mid-level.