Pretty solid, though my experience is unfortunately limited to singleplayer - the free-to-play period was too short! There wasn't enough time to organize a time to play with friends!
It's clear that co-op is what it's designed for, and most of the gameplay issues I had would be resolved if I weren't in singleplayer. From what I was able to experience, I think it's pretty fun.
I did also struggle with graphics performance though - I don't have a great computer, so it's true that it's usually sub-optimal anyway, but most games aren't as bad as this. I had to put every setting to minimum and even resolution at the lowest that I could barely make things out - all to get a maximum of about 30fps, often lower, about 15 at worst. I've noticed early access games giving me a harder time than usual, but I don't know if it's because it's unoptimized, or if it's just because they're *newer* and I'm trying to run them on an older machine.
The visual design is rather good though, if you can handle higher settings.
Sound design is also good, almost *overdone* with all the bassy sound effects.
XD Main theme music sounds just like a No Man's Sky track.
Spaceship controls are good once you get the hang of it, though aiming feels harder than it should (but that's probably just because I'm not good at it).
On-foot gameplay is decent as well - though again aiming is rather difficult - and is pretty similar to what I'm used to. Halo is the only other first-person-shooter I've played significantly, and similarity to it is certainly a good thing.
Overall, great potential, but I don't think I'll buy it just yet - I need a better computer, and time to organize friends to play it with.
