Titan Quest has been compared to classic PC Action-RPGs, most notably Diablo. I'd say this is a fair comparison, but hardly one to think less of Titan Quest for. Besides more time spent in the first region of the game than necessary, everything about Titan Quest is perfect.
Characters are fully customizable; players can elect to play a hack-and-slash fighter, a nature-based summoner, archer, and more, and can combine talents from multiple skill trees to create any combination of character classes.
Gameplay is solid and polished, plus I found Titan Quest to be a bit more challenging than Diablo and similar titles. Ragdoll physics are a nice touch, and let a character literally bat enemies around if they are significantly weaker than the character. Graphic details are top notch as well, and work to make the game much more immersive when combined with the physics-intensive gameplay.
For fans of Diablo and similar titles, I can say Titan Quest is a must-have. Recycled gameplay is easily forgiven due to the extreme level of polish that has gone into this game.