You think a game using Titan's Quest engine and following Titan's Quest character progression system, and based on Titan Quest in general resembles Titan Quest more than it resembles Diablo 3? Interesting opinion!
It definately doesn't have "fancier looks" than Diablo 3. I mean...it looks like Titan Quest... Just slightly improved. What makes it stand out is all of the improvements added on top of the basic idea of the previously mentioned game. Grim Dawn is far more complex than it meets the eye at the beginning. Some fairly original ideas like items granting actual active abilities, among the more interesting ones. For a "mostly" single player oriented game it offers a lot of replayability which most games like that do not.
If i could compare it to something it would be a mix of Titan Quest (duh!) and Dungeon Siege 2, which is still one of my favourite hack & slash games out there. Before someone mentions it, Dungeon Siege 3 is just a joke that ruined the "legacy" of the series and is to DS series what Sacred 3 is to Sacred series.
But that said, people behind Grim Dawn definately deserve some heavy props for their product. I hope they will continue to release similiar games in the future, cuz they are damn good at it.