The gameplay of Titan Quest isn't much different from Diablo II -that's why it earned it's label as a Diablo clone, it's simple and fun. However, you can combine two different masteries and create a whole new class from it. Currently, I'm playing a Soothsayer (Nature/Sprit Masteries). If compared to a class in Diablo, I'd say it's a cross between a Druid and Necromancer. Right now, my Soothsayer can summon 2 Feral Wolves, a Liche King, and their health is boosted by the Heart of the Oak enchantment.
So there it is, my module will be delayed...again. Though I don't think my addiction to this game will last long as it did with Diablo II (which lasted a year). I'm certain that Jade Empire: Special Edition, which is just around the bend, will overshadow this game.