This is a surprisingly entertaining game. I have about 70 hours in it now. One of the nice aspects is that you can play co-op with up to 4 players, so you can quest together. Any progress made or items obtained are for keeps, and are not specific to the session, which is nice.
The web site explains the game modes better than I can:
http://www.grimdawn.com/guide/settings/gamemodes.php
You start the game in Normal mode (although if it’s too easy you can enable or disable the Veteran setting, which increases the challenge somewhat. Recommended for co-op). Once completed, you can start the game again in Elite mode, keeping your character & inventory. And once you’ve done that, you can restart with Ultimate mode, which is a fair challenge. Very much like Diablo. The graphics are very good too.