Monolith has released some actual gameplay footage of their upcoming console MOBA, Guardians of Middle-Earth, highlighting Gollum and Gandalf. Both will be playable in GOME, of course, and they're really just two of the 20-or-so Guardians available with the game.
Going by the video, Gollum is actually one of the tougher characters in the game. His difficulty rating is fairly high, and not surprisingly, survivality isn't his strong suite. That said, he can dish out tons of damage (he's referred to as a "Striker" in the video), and his agility allows him to move quickly around the map.
Gandalf, on the other hand, is an Enchanter type. He can fight with both a sword and staff, and boasts fair survivability. His damage output is also pretty high, not surprisingly. Check the video to see the two in action.
Battle Profile: Gandalf and Gollum - YouTube