It's pretty good
When I first started this up, I was expecting just another brawler-type game. I thought it would be another one where you just chose a generic character who was no different than any of the others and played in an area randomly generated from a list of generic arenas. I thought there would be a small list of pointless guns where everyone knew the rocket launcher was the best so they'd all race for it.
But I was wrong, and for one of the few times in my life I was glad to be wrong. In Newgrounds Rumble, you get to play as one of many iconic characters in the NG universe, a feature I most appreciated. Each character has their own upsides and downsides, and they actually make sense. It sounds perfectly normal to see that Tankman can do very high damage, but moves very slow. The gameplay is fast, usually being a fight between two players. I've only played the Pico campaign so far, and I loved every moment of it. Unfortunately, it was too short, the whole campaign of him being three fights.
Also I noticed one problem with him, and I don't know if it exists in the other characters or not. When I was fighting his last enemy, it became ridiculously easy to put my opponent in the air with my attacks for long periods of time. Thus I was able to "juggle" about half of his health away during the battle, while the rest of the time he pretty much just blocked.
I'm not saying that this is a bad game, no, not at all. I'm just saying it has some faults, but hell, almost all Flash games do! This is definitely an amazing experience that Flash gamers should not miss.