I just read a review and tried the browser based MMO https://Hordes.io
It is a lot simpler than the typical OTG games. But for a free no install game it is oftly cute. I am playing a shaman named acie send a tell if you try it out. It does encourage grouping having a tank, healer/buffer, and magic dps, and a bow dps. It appears to be voxel based.

This is a fun distraction. Started a Shaman (BadHealz) last night and after a couple of hours of game play was at lvl 16. Up to about lvl 10 I was pulling single mobs and killing them slowly, then I watch some guy just a couple of lvls above me train at least a half dozen mobs then kitting them and killing them without ever getting hit. The next 6 lvls went pretty quick after that.

Definitely worth a try if you’re into these games.