In my humble opinion, this is the greatest ARPG ever created, enhanced by the fantastic mod support that the community has used to the fullest. The class system is amazing, allowing you to combine two out of nine mastery trees to make your own unique class with an incredible amount of customization. You have the fully offensive, close-quarter mastery Warfare, which revolves around duel weidling weapons and becoming a whirlwind of AoE and single target damage, at the cost of defence. Ranged masteries like Hunting which allows you to deal huge amounts of damage from a distance, and debuff your enemies defences. Magic masteries such as Spirit, which allows you to drain the life from your enemies! And 6 other unique and exiting masteries.
The world is vibrant and beautiful, starting in Greece, them moving to Egypt, then China, and with the DLC, even into the domain of Hades himself! The quests while perhaps a little generic, are very fun and easy to follow, and often give satisfying rewards along with a nice chunk of EXP and Gold! Not to mention the amazing loot you will find along your journey.
All in all it is a wonderful game, one of my all time favourites, I highly reccomend checking it out. And if you enjoy it, keep an eye on Grim Dawn, a game being developed by many of the same people that made Titan Quest, it promises to be an equaly enchanting ARPG set in the Victorian times!