This is one of the best games for iOS period. It only got better with the legendary edition. Due to the Mastery system there are about 50 main classes you can experiment with, and many possible builds for each class. Combine that with different equipment options, that you can customize and share among characters and the replay value is almost endless.
The only minus point I can think of is that Game Center does not have all the steam achievements, such as I have pets for that where you finish the normal difficulty with fewer than 100 kills.