Anyone playing on apocalyptic?
 
I'm finding the bat somewhat tough, not too tough but I'm starting to grow concerned that the difficulty is gonna spiral up and out of control.
 
Can't decide if I should start over on normal and just enjoy the ride, or continue on hard and risk it getting out of my "enjoyment zone".

The bat is by far the hardest enemy in the game imo.... 
Well ok thats not true... but he's a real whore... Once you level up the Harpoon ability, things get much easier. (I use it, instead of dodge, you move further, and faster.)

I'm playing through on Apocalyptic, and I am currently looking for the seven shards of the Armageddon Blade.  Tiamat was definitely beast, but there's patterns to it all.  Once you know the patterns, it gets easier and easier.  Is it difficult?  Yeah, you're going to die more than usual, and things take some pretty nasty damage and keep kicking ass.  However, it's not anywhere near impossible, and completing a boss fight over even a small battle against five or six common enemies feels totally satisfying.  Get used to having little to no life, though.  Some of those common enemies, without Armorskin active, can hit for two lifestones worth of health!!! 
 
Personally, on Apocalyptic, I think the toughest boss was Tiamat, though.  Silitha can be a bitch if you don't have your timing down well for the dodges from her claws and the abdomen slam, but other than that, definitely Tiamat.  Straga wasn't a walk in the park either, but it took me less than a hour to beat him. 
 
**I should point out that my Apocalyptic playthrough is my first playthrough as well, so if that helps any.

I decided to treat this like I did Batman, play on Normal to get the hang of the combat/timing (even if the actual difficulty doesn't necessarily require that depth of play), and then come back through on Apocalyptic when I have a better idea of how to handle myself. Hopefully I'll be able to get the Abyssal Armor as well to help on my second playthrough. I just am not interested in having frustrations on my first run through. I wanna go through, enjoy the story and then challenge myself when I'm a bit better prepared for what I'm going to be facing.