Castle crashers is a side scrolling, action adventure RPG by developer "The Behemoth". If you've ever downloaded the trial of this game, you'll know that it's under 200MB. But this game has a large world to explore in the style of the map world in Super Mario Brothers 3. Each stage is a good length, with humour and great combat along the way.
You choose which knight you're going to be on a select screen, with the key difference being different magic attacks. Red knight can do lightning, Orange knight has fire attacks, Blue knight has ice attacks, Green knight has gas attacks, and the free downloadable character the Pink knight has rainbows...no joke. After you've selected your knight, it's time to start the game.
The plot of Castle Crashers is as simple as a bread sandwich. You're a knight in fashionable, shining armour, who has do to the standard "go save the princesses", each from a different villain. (There's four princesses, like one wasn't enough).
Even though there isn't much of a plot, the game is very good at setting an atmosphere, even with a cartoon graphical style. The game starts with you're character in the castle, having a good time, when suddenly the door busts open, and a grey knight tumbles down the stairs with an arrow in his spine. This helps set the, "Sh*t's going down" atmosphere. as you wander into the castle courtyard, with sword and shield in hand, barbarians are attacking, and houses are burning, keeping the theme consistent, and the atmosphere can change throughout the entire game. For instance there's a forest level, where you hear loud stomps of a creature, and whenever another animal hears these sounds, they evacuate the content of their bowls with the ferocity of a spaceship. Letting mystery and humour mix for a short period of time.
The combat is like so many other side scrollers, move in a direction, kill people along the way, repeat, but castle crashers at least attempts to mix things up with pets. Pets can be found in the wild, and each pet grants different abilities to the player, some pets allow you to level up faster, some will make your attack or defence stronger, some can find and retrieve items for you, and some will just join you in combat, but they don't hit very often, waiting for your pets to attack is like waiting for a socially awkward teen to deliver bad news to an elderly woman. It takes too long! And when the pets finally attack, there's probably only a few enemies left, or they miss, which is very anticlimactic.
Overall, Castle Crashers is a fantastic game, and very cheap, so if you have a some spare time and cash, give it a go.