Truly an innovation in Multiplayer Arena games. I bought this game back before it was free-to-play, and even though I've set it down for quite a while, I don't have an ounce of regret concerning the purchase.
This game brings the best of MMOs, MOBAs, and FPSs together. Forge features nicely decorated maps and characters, a new and fluid combat system, and a variety of characters with unique roles and abilities. Although frustration is easy to encounter when first starting out with Forge, once you've rebound your keys, figured out what the plethura of abilities that your favorite character offers can do, and put in a little bit of time to learn how to succeed in the game against more experienced players, it offers an amazing multiplayer gaming experience that can't really be found elsewhere.
If you need a game to reference, Chivalry: Medieval Warfare is probably comparable to Forge, but perhaps a bit dumbed-down with less focus on abilities and more focus on intense combat with variety seeded in weapon-choice.
Forge combat usually plays out like your typical MOBA battle-a series of stuns, bleeds, poisons, blinds, silences, stealth/invisibility-moves, etc.-, but Forge adds an entirely new dimension to the combat with the third-person perspective and FPS-like implementation. Everything about Forge combat feels good, and when you shoot an arrow to pin an opponent to the ground, you feel like you're actually making a physical impact in 3D space.
Not to mention that the movement system includes wall-jumping built-in. Any character can jump from wall to wall like a lemur at will, given they have enough "energy" at the time. This adds to the fluidity of the fast-paced action. Even height becomes a relatively small barrier to the continuous movement that becomes second-nature as you familiarize yourself with the game.
Forge gets a bad rap because the community isn't exactly active these days (as well as the fact that the game can be rough when you're just getting started, for reasons mentioned above), but if you can get some friends together to try the game out, I would recommend it (but perhaps it'd be best for some preparation time beforehand, as the tutorials do take a bit of time and it takes some time to adjust to the gameplay and find the keybindings you like best). I hope that eventually this game will have a thriving community again, which Steam has provided for so many other unique multiplayer games.