I like it as an alternative to GNOME that's not quite so GNOME-ish, if that makes sense. I do like GNOME but I find it a bit idiosyncratic sometimes, IE they seem very "my way or the highway" about some design things, and it often feels to me like you have to hunt down and keep updating endless plugins to do basic things that feel like they should be included.
If they can land in a spot where COSMIC looks as nice as GNOME but is also a bit less of a hassle to get set up the way you want it, I feel like they could occupy a nice middle-ground between GNOME and KDE possibly.
Yeah I've been running it in one of my little VM specimen jars for a while now and I don't remember it crashing or doing anything weird so far. Pretty good for a first alpha!