This is because on the one hand, the budget and on the other hand the long-term motivation. In terms of graphics, effects and physics, diversity of skills and classes, story and staging "Responsive" -ness proposes Diablo3 TL2 without question by far. Sure you will not do justice to TL2, sometimes applying the standards of Diablo3 with a gigantic budget and several years of development with a much larger team of TL2. And without question TL2 still fun, but in a direct comparison can not keep up in the above points.
The second point, the long-term motivation has always been a big plus the Diablo series. And Diablo3 has laid the last patch the foundation for years of fun. An Endgame as in Diablo3 missing in TL2. Clear, we are talking of hack-and-Slays and not of MMOs and TL2 has in its manageable by season certainly a big plus for Casuals. However, it was precisely the long-term motivation that has made D2 to what it was: a successful more than a decade Action RPG that has not yet addicted, even after hundreds of hours of game time. This status comes D3 with recent patches at least closer.
Unfortunately, I wrote in the review more about Diablo than Torchlight itself, but I hope that it helps many Diablo2 veterans when deciding between D3 and TL2. 3 star corresponds to "satisfactory" overall impression of has set in after one playthrough. A positive feature is particularly the creepy-brilliant soundtrack by Matt Uelmen which was formative for Diablo2, TL1 and other senior Blizzard games. This is also the point where TL Diablo3 is superior. The best is of course to play both games. It is well maintained in both.