Titan Quest is exactly like a Greek version of Diablo 2/Torchlight 2.You journey from one location to the next rather than delve into tiered dungeons like in Diablo/Torchlight, which is nice, esp. with the very well-done environments. Also, instead of several areas with loading screens between them, the game is played on one huge map, including the mini-dungeons scattered around the map. The Greek/mythological aesthetic is welcome, seeing as the only games that take place in this setting systematically defile it (I'm looking at you God of War) or are Stategy games.
Sadly, that's where the praise ends. Every enemy is practically the same and drop absurd amounts of "broken equipment", which basically means crap that's worth nothing and unnecessarily takes up space. That coupled with the already pathetic inventory space makes this game an annoying grindfest, where one battle can result in as many as 3-5 trips back to town. The stat system is a joke, and the 3 main attributes barely affect anything besides equipment requirements. Their are 8 "Masteries" or skill trees, of which you can only select 2. Not that you want more, seeing as you need to pump points not only into each individual skill, but also into the mastery itself to unlock everything, and seeing as you only get 3 points per level and both the skills and enemies are already a joke, you might as well not even try. Which is good, because the developers reached the same conclusion as well, and made leveling up take forever to do. I've played around 8-9 hours so far, and have JUST reached level 10.
In conclusion, Titan Quest is a good-looking, but VERY flawed game. It suffers from the same problems Diablo 1 & 2 did before, and shot itself in the foot with some particularly BAD game design of its own. If you want a good action rpg in the spirit of Diablo, play Torchlight 1 & 2. However, for as many complaints as I have about the game, it is worth at least one playthrough for the setting, which it pulls off nicely.