Titan Quest is the greatest Hack and Slash Diablo-clone I've played. It should not be missed by RPG-lovers.
TQ has better graphics - variety of environments is simply amazing. I felt that I am also present at Greece, Egypt, Orient. All of the locations are amazingly designed and beautifully presented on the screen. Every map has unique atmospheric feeling.
Characterization for the protagonist is better than Diablo2 but not much customizations are available like BG2 or NwN. Still you can become a distinctive character for second-time play.
Weapons, spells, skills are full of variety that gives your character a unique experience. Boss-battles are really really tough.
Story-wise this game is cool. You'll never feel bored from the continuous chase for enemies and quests.
Overall this game is fully enjoyable. Anybody loved Diablo2 should not miss this game.