Just played Survival Nation for about 2 and a half hours co-op. It's very confidently and firmly "good". Feels like an MMO with how the enemies spawn in clusters, the map-marked gathering spots, and how the map is laid out. We got one random guy joining us too but he didn't have a mic or stick around for long.
Melee combat has decent impact and isn't wet spaghetti. Guns are good to shoot though reloading is a bit weird without having like a physical ammo pouch. Climbing is crisp but you can't throw yourself. Enemies aren't terribly varied but do have a couple of different types. The enemies also have levels like borderlands so you might stumble onto some high level enemies and get fucked if you explore too far. Crafting is just a menu though it's straight forward and not convoluted. UI and controls are perfectly fine but again are menu based rather than physical slots and holsters (similar quick menu to alyx).
Everything about it is okay so other than there being some other game that does each feature better, it's hard to find anything overtly wrong with it. One good thing I was worried about to start is that it definitely has a lot of stuff in it. Pic related is the map as zoomed out as it goes. There's a whole city area south of the river so what's shown is about half the total map. Marked area is the area we explored in over 2 hours play time. I recorded the whole session so I'll slice up some webms tomorrow.