Castle Crashers
I've had the chance to play this at a friend's place a few times, and I came away a lot more impressed than I thought I'd be. Castle Crashers is a modern Golden Axe with Flash-game-esque humor and direction. It isn't a perfect production, and inherits some shortcomings from its genre, but is nevertheless extremely fun in the right circumstances.
Superficially, Castle Crashers is a multiplayer beat-em-up. You and up to three other players suit up from a bevy of selectable characters (there are only four at first, but playing through the main story unlocks more to choose from) and set out on a quest to save the King's magic crystal, and his daughters, from evil demon alien shit. Along the way you'll travel through ravaged battlefields, grassy plains, barren deserts, a volcano, and even a space ship, among other locales. The game's campaign is split up into discrete levels, such that your progress is saved incrementally and you can pick it back up anytime. There are occasional moments where I would really, really have preferred an extra checkpoint to avoid repeating ten minutes of enemy bashing, but these are fairly infrequent. There are also a few places where the path branches, although this is exclusively for the purpose of seeing that Path A is locked and finding the key at the end of Path B. Anyway, the ability to save is a much-appreciated improvement over traditional beat-em-ups.
Another thing that sets Castle Crashers apart from its ancient brethren is the RPG experience. The engine driving the game is experience- and ability-gaining, with a healthy dose of collectible and consumable items (weapons, helper pets, health potions etc.) thrown in as well. Attacking foes - be it with a weapon, a magic spell, or a bow and arrow - nets your dude experience points, and at every level you'll earn skill points to invest in Strength, Magic, Defense, or Agility. Where Strength and Defense will only increase your physical damage and health, respectively, Magic will increase your MP regeneration rate and give you new magic attacks; and Agility will increase the range, speed and damage of arrows, in addition to your normal running speed. You'll also learn new combo attacks at certain levels, if you're into that sort of thing.
Enhancing this robust customization is the fact that each character has a unique talent (although some unlockable characters copy magic spells from other unlockable characters, there are still a bunch to choose from). Red Soldier, for instance, has a sick lightning spell that can unload on foes continuously. Green Soldier can poison guys, and Yellow Soldier can light them on fire. Blue Soldier can freeze them! Each of these magic spells, and their companion moves which come with more Magic points, encourage a particular character type toward certain skill allocations. But, since each character can only be selected once in a single game session, there is no risk of overlap in a given game.
Local multiplayer is incredibly fun, and there is also an online multiplayer option (though I haven't tried it myself). However, this is the kind of game that is really only fun with more than one person. You might play by yourself to improve your guy somewhat, but unless you're trying to catch up to your friends, it's really just an exercise in tedium as you slash away at hordes of enemies on your own. More than just typical party-game flair, multiplayer games allow the unique characters to complement one another's skills, and so having only one skillset makes for a pretty boring experience.
With that said - and the caveat that there are some frustrating collision-detection moments, due to the game's paper-thin hit boxes - if you've got someone to play it with, Castle Crashers is an absolute must-try. It's cheap, it's very fun, and I wouldn't be surprised if it continues to be fun into the foreseeable future.
Progress: Gave Up -- Beaten once, Red Soldier is awesome