Titan Quest is a refreshing experience after Diablo 3. Make no mistake: I liked Diablo 3 a lot but it was certainly a bit too casual for my taste. Titan Quest brings back the good old skill tree concept. There are no races here - you just pick the skill tree at the beginning and after several level-ups you can pick another one (the game refers to these as masteries) and as a result of this combination you will have a class.
I'll give you an example: you want to be the expert of close-combat, an expert of swords and other melee weapons. You pick the mastery called Warfare for this purpose. At the same time you would like to summon spirits to aid you in combat and throw molten rocks at your enemies or utilise other earth magic spells. You pick Earth and there you go you have just become a Battle Mage. Overall, you have 9 masteries so you can guess how many combinations you can have. This gives us quite a high replayability value.
Other than this the formula is pretty much the same as in Diablo:
--the story is divided up into various Acts which all end in a boss battle
--you have places full of enemies but you can rest in towns; these give you opportunity to pick up quests and visit vendors for purchasing / selling items you acquired by looting
--you kill then you loot: rinse and repeat!
--you level up and spend points on your main attributes and skills points on your skills offered by the masteries you picked
--you get to loot many items and weapons' strength is indicated by their colour; you have legendary and set items here and you can further enhance your weapons by inserting charms and relics into them
--while you are getting stronger you are expected to find items that add to your elemental protection
One of the criticism regarding Titan Quest was that it was too similar to Diablo. But if you have a decent system that works quite well why is it an issue to have it copied? The creators simply thought these were quite good in Diablo so they only changed the skill variety which I believe is commendable.
Also, the environment is a bit different as the game takes place in ancient Greek so you can expect monsters from that mythology. Act 4 is simply jaw-dropping with its River Styx and the City of Lost Souls.
The game was released back in 2006 and its expansion pack a year later. Still, the game looks good and it utilises Havok physics quite well. One interesting thing, though: the game does not generate a new environment once you restart it, not like in Diablo. So, should you replay it with another class or on another difficulty (these get unlocked after game completion - again, a similarity with Diablo) all environments will look similar.
I liked Titan Quest. I played it after Diablo 3 and for me it was refreshing. I liked its environments with all the mythological creatures. With the 4 Acts you have at least 40-50 hours for one walkthrough on normal difficulty. I say that's quite long considering the high replayability and the multiplayer option available.