Torchlight 2 is the perfect sequel to the original game.
I recommend playing the game on hardcore, this adds a lot more thought to the game and keeps you a lot more interested in the game.
The games GUI is clean and the steam-punk graphical style is really well matched to the gameplay and classes.
Your companion throughout the game is your pet, you can choose any pet from a collection of 10, ranging from dogs to headcrabs. The pets are very useful in the game as not only can they attack enemies, carry loot and cast spells. They can also be sent to town to sell the things in their inventories and even buy items like potions and scrolls.
I really liked the leveling system in Torchlight 2 because, although there are different abilities trees you're not locked to a certain one and don't have to go through a whole tree to get an ability at the end of the tree, this creates more variety and gives you a lot more choices of how you want to play your character, you can go a 'Jack of all Trades' or just specialise in spawning robots as the engineer, or using fast, duel-wielding attacks as the beserker.