I think it's better than D3 in some ways. It's basically more of the same but there are less of the annoying things that spoiled D3 for me like monster closets, and the frequent instances where you grab a pick-up and monsters pop out of nowhere and attack you. Those things have been almost completely done away with but it still relies on monster beam-ins. I suppose it makes sense that creatures with that ability would ambush you like that but I just find it cheap and unimaginative gameplay design.
It's just as spooky as D3. Atmosphere is what this game has in spades. There are a few new monsters but they're mostly bosses. I don't find bosses very much fun. They're ridiculously hard and always rely on some weakness that you have to exploit to kill them. ROE takes that to a new level. By the time I got to the third boss (which wasn't even the end one) I'd given up and put it on God mode. The other new creature looks freaky but is basically an Imp Mark 2.
It's quite a bit more challenging than D3 (I actually ran out of ammo once or twice on Marine setting) until near the end when it gets so hard it's funny. I get the impression the devs didn't want me to finish and were just trying to kill me. In the end I went back to God mode, then it was just a boring slog until the final battle, so rather a let down there.
I found it quite long for an expansion. Claims that it's very short are greatly exaggerated. You just have to remember it's an expansion, not a full game.
Basically good, solid, spooky shooty bang-bang game.