I think the biggest problem right now is the hyper-limited Campaign Toolset. That said, N-Space has said they plan to update it with branching dialogue and larger text limits (right now you can only add text to an NPC via a "quest action - give, update, complete", and only 3-5 lines).
As for the mechanics, it plays more like D&D than Diablo by far - I suspect people who are saying it's "Diablo-like" haven't played Diablo in ages, and are misremembering how it worked. For one thing, you don't have click-per-attack like in Diablo and other ARPGs. Secondly, you can pause and even auto-pause every round, in multiplayer (and it works fine).
If they fix the toolset up some, I think it will be good fun for dungeon crawling and some medium-complexity campaigns. No, it won't be like having a v-tabletop with a rules engine, but I don't think that was ever on offer anyway.