Rage 3 is a pretty straightforward stick figure beat-'em-up, which is apparently a pretty popular genre on Kongregate. Fortunately, it's significantly better than the last game of that type that I played, Thing-Thing 2 (review here), but it's still not the world's most exciting formula.
So, you're a stick figure, and you're angry at other stick figures, for some unspecified reason. You go around and beat them up with either a variety of melee weapons (mostly variations on a sword) or a variety of guns (which I ended up almost never using, because I didn't need to). As you beat people up, your rage meter fills; once it reaches 100, you can unleash various rage attacks. That's pretty much it. Defeated enemies drop brightly-colored spheres which can recover your health or increase your XP; as you level up, your rage power gains more abilities.
In Adventure mode, you progress through four different levels, featuring the obligatory keys, locked gates, more weapons to collect, and so forth; at the end of the level, you fight a relatively simple boss. The locks and keys tend to slow down the pace of the game -- the first time through, there's plenty of enemies to beat up, but when you're crossing the level a second time in search of a key (or after having obtained the key), there's not much to do, which makes the level kind of boring. It would be much more interesting if there weren't these dead spots. The game is thoughtful enough to tell you what a key does when you pick it up, so at least you know where to go. However, a truly terrible design element is the presence of gates that you have to be a certain level to pass -- this requires you to do some mindless grinding in order to beat the game, which is not what I'm looking for in a fast-paced beat-'em-up! There's also Arcade mode, which is just a never-ending succession of enemies, which is a good place to level up if you need to but not really exciting beyond that. Oddly, the game doesn't autosave; you have to go back to the main menu and choose to save yourself in order to save your progress, which I'm sure can be quite annoying if you forget (fortunately, I didn't).
The animation is not bad; it's smooth, and there's a fair amount of variation, but pretty simplistic -- for instance, when you're fighting an enemy at close quarters, there's no change in the moves that you use. The graphics are, well, stick figures, though the various maces, swords, and other weapons are lovingly rendered. The sounds are pretty much your standard assortment of hitting noises. The music is not terribly exciting, but it's a good background which adds a bit to the game without being horribly repetitive.
The game is extremely easy -- at least, if you're playing on the easy difficulty level, which is apparently the default, as I discovered halfway through. By then, I didn't really want to bother trying at a higher difficulty, so I finished the game without any major difficulty. I'm not a big fan of games not asking you for the difficulty, so I was a little annoyed by this decision. Overall, Rage 3 isn't a bad game if you're just looking for some mindless bashing/stabbing/shooting action, but don't expect very much more than that. It's good for a few minutes of silly fun, but isn't the kind of game you'll want to play again and again.