Let's get this out of the way, is this game worth buying even in Early Access? Yes.
Why? Well, first of all, it's further along than most early access games. I've already put over 40 hours into the game and still haven't seen most of chapter 2. The amount of content is huge.
But while content is king, gameplay is God for most. The easiest way to describe the game is to compare it to Titan's Quest, but improved. It makes sense since Crate Entertainment is made up of some of the same people who worked on Titan's Quest. It's also built on the same engine, though that's been improved too. The art style is more how I wanted Diablo 3 to look, and I absolutely love it.
Unlike Diablo 3, in Grim Dawn you can have two skillsets or you can just stick with one, but each level only gives you three points to spread over the skillsets, so you have to choose. You also are able to choose your attribute points, though there are only three choices. It's simplified, but not to the point of Diablo 3.
The game has a faction system that looks like it could be promising later on, but at the moment it's simple and mostly meaningless. You gain fame and reputation through killing big bosses and monsters which can open up other side quests, but you'll usually open these up just from playing normally and not paying attention to your fame stats.
I dropped $58 on this game during its kickstarter, it was money I had saved for Diablo 3. I don't regret a penny, and after picking up Diablo 3 on sale, I think I made the right choice.
But, it is in early access so there are chances for bugs. I haven't ran into any since they've released Act 2, but keep in mind it's still a work in progress, but even then it's better in my opinion than some full release games.
If you love ARPGs then you owe it to yourself to pick up this game, especially when it's only $25.