In fact, as much as I detest "it's like this but this," I feel like that's the best place to start. The best way I can describe Cobalt (the first third-party release from Minecraft's Mojang) is as a curious mix of John Woo, Super Meat Boy, Contra and (most prominently) Super Smash Brothers.
Like I said ... a lot going on.
You control a diminutive, adorable, blood-thirsty robot battling others of your kind in a 2D, neon-drenched battlefield. Aside from the weapons all robots have at their disposal (batteries, hatred of flesh-men), these bots have a fast arsenal of explosives, energy weapons and good old fashioned robot punching.
While the modes I played at PAX were pretty conventional (capture the flag, death match), their pace was far more accelerated than what you'd expect. Kills and captures happen fast, and one well-placed grenade can turn the tide.
It was clear that there was definite method to this robotic madness.
In fact, the only time the game slows down is when an enemy projectile is nearing one of the bots. As time slows, the bulky beam or bullet is highlighted, and the target has just one chance to deflect the shot by rolling into it (cool) or punching it away (supremely cool).
The effect of this slowdown is that a bunch of players meeting in the middle of a map quickly transitions into a slow-mo gunfight that could be accurately described as a bullet ballet if the robots weren't so stubby and if a large number of the "bullets" weren't rockets/grenades/energy beams. It may not be elegant, but it sure is a heck of a lot of fun.
Though chaos defined my brief play time with the game, there seemed to be deeper systems that players could explore as time goes by. In fact, I was unable to finish the "advanced tutorial" which taught moves like getting more grenade distance by throwing mid-roll.
While the speed and frantic action was a lot to wrap my mind around in a crowded expo hall, it was clear that there was definite method to this robotic madness. I for one am looking forward to exploring it when the game arrives on PC, Mac and Linux this fall.