Hmm, seems like it has the potential to be a fun, goofy brawler, but in its current state, it's more like an early alpha or prototype, lacking a unique angle or significant pizazz.
As said, there's a decent foundation here: I like the different arenas and running around chucking objects at each other and all that jazz. But the game always seems to devolve into a messy brainless mashfest, as the movesets don't seem to have any sort of real strategic depth to them. Why bother blocking, for example, if you aren't able to gain any sort of advantage against an attacking player for making a smart decision? You may as well just attack him as well and slap it out. Would definitely love it if characters had their own special moves, and if the arenas had special events that would happen to help increase the chaos and push players together more, such as meteors raining from the sky in the UFO level and so on.
I realize that my feedback probably isn't ideal because I came from this at a single-player angle, but I still think most of it is applicable. Still, something to consider, as human opponents could change some things around (but not that significantly, in my opinion).