Ok, hasnt really been a thread about this that I can remember, so I figured I'd start one.
The point of this is to post thoughts on either individual monsters that could do with some tweaks, or on the balance of a certain biome type as a whole, depending on which enemies appear there. The problems with the laser spiders are already known, so I'll skip those. I'll start with just a few here based on my latest session with the game.
1. Flying Eyeballs: Reduce their health.... seriously. These guys are alot like mosquitos in that they're incredibly difficult to hit, and unlike mosquitos they drop lots and lots of those bombs. The attack pattern doesnt need changing.... just their health level, particularly if they are to remain common like they are in the craggy zones. Aside from the spiders, this is probably the one enemy closest to being "broken" right now.
2. Urban Robots: If that's the correct name, I forget. The little guys on wheels that fire the splitting orange bullet. Like the eyeballs, a bit too much health on them, so it gets kinda tedious to take them all out. Considering the strong splitting shot, AND the ability to counter-attack, these guys definitely dont need a ton of health to put up a fight.
3. Clockwork Avian: Again not necessarily getting the name right, but it's the bright yellow-ish bird that just charges at you. A suggested change to these guys is simple: have them make some sort of noise or something when they approach. These guys can lead to some cheap hits currently, particularly in level-up towers, with the fact that there'll be nothing there for awhile, and then very suddenly one of these is on top of you; the player character isnt quite fast enough to dodge these guys by pure reaction. They're fine otherwise.
4. Sphinx: This one is very simple: take these guys out of caves, specifically. When they appear in a cave, it's most often in the sort of slice that has a super-low cieling, meaning there' no room to jump over their ice attack when you're up close to melee them.... you're pretty much forced to either take some damage, or waste ammo. They're totally fine other than that one problem.
That's just a start, the ones I can think of at this moment. I'll have more to add to this list later.