I finished it. Damn, this is really great. I love the game so far, really can't wait to play the rest. If this is any indication of what's to come, then we have an excellent Build shooter worthy of the Holy Three. The level design is kickass, multi-layered and on a grand scale, the game looks great, the one-liners are pretty good, the weapons are awesome, especially the homing grenade which is a lot of fun (though I'm not a huge fan of the SMG), and the music is fantastic. The monsters lack a bit of variety so far, but I imagine there will be a lot more later on. The smoke effect that comes with the explosions can tank the framerate when there's a lot, though.
The first level is enormous and the game can become quite difficult even with secret items.
That's...a bit ridiculous and indicative of easy game difficulty. Each secret is a reward, which therefore makes the game easier. So the game better be designed around finding a portion of these secrets mandatory, or make it so they don't all reward health and ammo and other such major difficulty economy influencers.
I won't say anymore without having played it though.
The first level is enormous and the game can become quite difficult even with secret items.