Generally its because you've ignored side missions. The Wildlife Preservation Area has a huge level jump and those Rabid Stalkers will rip you a new one quite easily. Its not so bad if you've been doing all the sidequests up to that point but on the second playthrough it is very tempting to avoid it.
Saturn is a tedious boss rather than a hard one. It has a silly amount of hp and everything it does can be easily avoided by staying by cover/circling the house.
the hardest yesterday was the 4 badass commanders at the bottom of the lift shaft ( mortar), i got Goliath to kill them for me.....but Mortar later on was easy, because i got yet another Goliath to kill him as well, because normally he's a nightmare

the rest of bloodshot was easy, it's just a case of run, hide, run, hide and fight only when you have to !!!!
this is actually quite similar to the 2nd playthough, it's just that i forgot how hard it was last year.
you dont have to use **** first to kill them anymore, Zero seems ok now, he'll be the same as he was at level 50 soon, this will make the DLCs much more fun to play.
We must not forget that Zero was always Krap at close range, with Zero you have to stay back/cover.....so was Mordacia, the only thing that made him good at close range was a monster one shot kill Shotty, usually Jakobs 8500 or Sledge's.
that 8500 Jakobs will probably be by level 61 about 22 000, mine is 17 500 and still a bit weak, but it's only level 57.