GamersInfo.net has tossed up a review of Titan Quest, and while they don't give the game an overall score, they clearly liked it.
Overall I enjoyed Titan Quest and recommend it to those people who liked the character building and item hunting of Diablo 2 and other games of that style. It is a beautiful game with great looking environments, effects, and has a fantastic music and sound effects. The class progression and character building is indeed one of the strongest aspects of the game and one that could definitely help the longevity of the game in some people's libraries. But if you are thinking of playing the game looking for a great RPG or an excellent multiplayer experience, then I am afraid you will find the game lacking as these are not among its strongest assets. Finally, one area I did not get a chance to test out was the ability to mod the game. I know it exists and in fact there are guides released by THQ on the subject. Several editors ship with the game and are in the game folder, such as ArtManager, ModelCompiler, MapCompiler, QuestEditor and so forth so the game does appear to be highly moddable, which may also help increase its longevity among fans.