If you're expecting more than three character playthroughs for Torchlight, you should probably invest your gaming dollar and time elsewhere. While Torchlight mimic's the near endless replayability of Diablo II, a seasoned gamer will quickly see how thin the meat is on Torchlight's bones. The way it scales difficulty is uninteresting and boring. Although the game seems to have good reason to play through again, once you discover what makes Torchlight tick you'll be on to the next game.
Everyone loves a good boss fight, but each of the demons you'll face in the mines and dungeons beneath Torchlight have but one rote trick up their sleeve: extra beefy hitpoints. If you kick the difficulty up a notch or two, it even gets worse. On my first runthrough on hard, the final boss took maybe ten minutes to slay. I was a sword and shield Destroyer and I had fun whacking away at the gnarly monstrosity. When I kicked the game up to Very Hard, my Vanquisher had no trouble eviscerating hordes of demons with Exploding Shot. But when I reached the final boss? I watched my puny blasts whittle away slivers of a percent of his total health and in total probably spent 40 minutes of holding down the right mouse button to finish the game. That made me never want to reach the end of a play through ever again.
But Torchlight seems like it wants to encourage multiple playthroughs with its ancestry system. Once you finish up you can retire your current character (don't forget to stuff all your gear in the shared treasure chest) and while doing this you select one of your most cherished items to have it passed on to your sire. This item or weapon will be greatly enhanced and have reduced equip requirements so that you ideally will be able to use it early on with your next character. After my Destroyer, Maximo, retired his daughter Maxima had a really awesome Talon Coif to wear once she was able to. Unfortunately, since the game doesn't scale in difficulty in an interesting way I was forced to grind through the same game with just an inordinate amount of hitpoints applied to each of the monsters.
In a game like Diablo II, the subsequent levels of difficulty throw new tricks at you: altered enemy types, enemies that focus on specific elements, and cannon fodder that is physically resistant to your usual tricks. Its bosses are wickedly unique featuring attack patterns that don't change much on each difficulty level but each of the boss fights are always fun to return to on another playthrough.
Since just about each character class can use many of the same passive skills and can eventually use all of the same items it really becomes hard to differentiate between characters. Sure, your Destroyer can't summon Golems like the Alchemist but he can shoot a pistol as strong as the Vanquisher. The spells in the game are found randomly throughout the dungeons or purchased from a town vendor. I never even used spells except for town portal. They were extremely underpowered for me, nearly useless. Even for the Alchemist its best to just stick with the powers in your skill tree. For a while I felt like I was missing something, but no, spells are just pointless.
Torchlight features a ton of Diablo II charm with its own beefy character-style and fun graphical effects. But its lasting appeal is minimal at best. But for a game that you'll probably catch on sale for $5-$10 it is a fun diversion from the games that will really catch your gamer's eye. Just don't expect much challenge or lasting power and don't be sold on the concept of an infinitely deep dungeon. Because by the time you've reached the campaign's end, Torchlight's appeal will have fizzled out.