Doesn't seem like a very well-known game, I found it scouring mmohut yesterday, it's actually pretty damn fun.
It's a browser-based flash game.
Your objective in the game is to kill, as much as you can, i'm pretty sure once a certain number of enemies are killed, the game spawns the Mad God and teleports everyone in the dungeon to his room, once the boss is killed (while the boss is being killed) the dungeon resets.
From what i've seen so far, I can say;
--Pros
-NO download.
-Guest option to jump straight in the game and try it, or you can create an account.
-Dead Ops Arcade-style gameplay.
-MMORPG.
-Plenty of gear to find.
-co-op based gameplay, everyone works towards a common goal of spawning the mad god and killing him.
-Multiple classes, unlock advanced classes by leveling up the previous ones.
-Stash to put gear in that any char from your account can access.
-Hardcore-style gameplay can get the ol' heart pumpin' when you run into a nasty group.
-Plenty of people playing.
-Customizable hot keys.
-Ability to teleport to any player on the map by left-clicking their green dot on the map, or you can "lock" a player and teleport to them at any time with ease.
-None of the cash shop stuff looks like it makes characters over-powered.
-Pets.
-Built in autofire for those who want it.
-Ability to teleport to town instantly, from anywhere, with infinite usage.
-I haven't used it yet but, it supposedly has a permanent squelch feature for those annoying people who show up occasionally in mmo's.
--Cons
-First and foremost, when you die, your character is dead, you have to remake. However this does give you the opportunity to switch classes, class unlocks are saved.
-Mostly ffa looting, it isn't too bad though usually.
-Only 1 character slot starting out, you begin with 100 gold and the first extra character slot costs 600 gold.
-Only 1 stash box starting, each box is able to hold 8 items to switch between your chars, you can purchase additional stash boxes with Gold & 500 each.
-Gold is a cash shop thing, you have to pay real $ to obtain it, however the game is still perfectly playable without it.
-I deal with some lag, i'm not sure if everybody has to or if i'm just special that way.
-Level 20 is the max, however you can still find stat potions to finish maxing out your character and you can find kickass gear upgrades to take your char even further.
I may be forgetting some stuff but, that's most of what i've found out so far, it's a pretty good game..i'd suggest to anyone who likes that style (like Dead Ops Arcade) to give it a shot.
http://www.realmofthemadgod.com/If you create an account for it, you get a tutorial level, it auto-started me as a mage in the tutorial..i'm not sure if that's set or random.