The best replacement for titan quest is torchlight.

The best alternatives to titan quest are rated as following:
★★★★★  torchlight
★★★★★  diablo
★★★★  sacred 2
★★★★  diablo 2
★★★  diablo 3
★★★  immortal throne
★★★  sacred
★★  torchlight 2
★★  path of exile
★★  dungeon siege
★★  diablo ii
★  loki
★  dungeon siege 2
★  titan quest immortal throne
  grim dawn
  dungeon siege ii
  neverwinter nights 2

Your alternative for titan quest is not listed? Suggest!
Speaking about titan quest, one probably shouldn't forget about hamachi.

Other search terms related to titan quest and their ratings are:
★★★★★ hamachi
★★ immortal throne
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titan quest
torchlight
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