Crossbows are good, but you'll need something better to beat the throne, and it's easy to get overwhelmed with a slow weapon like that. It's also a really bad "oh shit" weapon, since there's a delay after switching to it and you'll often need to use terrain as cover to survive in a ton of situations past scrapyards, and you won't always have that luxury.
I actually like plutonium hunger, though at first I thought it was useless. The value isn't in attracting plutonium so much as attracting health and ammo drops. It makes fighting the throne without an ideal setup much easier, at the very least, and means you don't have to risk as much to grab desperation pickups. Hell, it might even justify the crown that makes them fade faster, but I haven't played around with that yet. I've never taken bolt marrow though, it looks worthless. Maybe something funny with disc guns could be done with it... I think it's possible to get two bolt marrow mutations as horror with an ultra mutation, just imagine the homing discs.
The level generation is pretty hit or miss, yeah. Sometimes you'll get spawned in a room where surviving past 5 seconds is really difficult, but I've never found it to be impossible, unless you've got really bad weapons. The levels also don't look great, I think the enemy design is much better done, even if I don't like pixel art.