I finished the game a couple of days ago. For the most part I really enjoyed it, with this game more or less stealing my attention away from Borderlands 2. However I found the glaring weakness of the game to be the final dungeon and end boss. I found the design of the final area to be really dull as it is just repetitious levels using the same tile set, with a rather bland mine design. It was also the first time in the game that I was able to identify separate pieces that were being stitched together to make the dungeons. Considering how nice some of the earlier areas were, this just seemed too drab to end the game with.
 
As for the final boss, I wouldn't say it was bad, but there were certainly much more well designed and challenging bosses earlier in the game. As I never finished the first Torchlight, did a similar occurrence happen towards the end as well?