In my opinion there is way too little story in Titan Quest. You simply go from town to town, fighting monsters in the wilderness between them. In each town there might be a tiny bit of the main story revealed - but then you're sent off to fight monsters for a couple of hours again. If you're looking for a game with a story my suggestion is that you pass on this one

EDIT: Just remembered a game that might have what you are looking for: Divine Divinity. If you haven't played that gem yet then I suggest you give it a try. The graphics might look a bit dated these days (it's from 2002 and in 2D) - but it's the best hack'n'slash RPG I've ever played! Lots of combat and character development, but also a huge open world with a solid main story and lots of side quests. Again - give it a try!