eh its really about the same, just bigger numbers as far as playthroughs go. the invincible bosses are definitely a step up from Crawmerax, seeing as I had an entirely legit gun that could one shot his critical parts. I feel like the loaders can't really compare to their BL1 counterparts the Crimson Lance soldiers, because those guys were badasses. Especially the corrosive troopers, which were hell to kill.
I feel like endgame is a bit tougher compared to BL1 though, solely because you can't find class mods with ammo regen on them aside from the gunzerker's hoarder class mod. I used to run a hunter with a 660 Gunslinger class mod with 4 revolvers and I could tear through anything with that no problem whatsoever.
A lying tongue hates those it crushes, but a flattering mouth works ruin. -- GT: Wretched Owls
I would say that the first borderlands is comparable to this one, but with less noticeable differences from level to level. With the first one, I never felt under- or over-leveled, whereas that's generally the case for me with this one.
I also find myself in fight-for-your-life more in the second, but I think that's the design of this one versus the first, and again has to do with how things scale with levels.
Overall, I guess the first one seems easier, but at the same time it seems to stay more at your level the whole time, so you still have to pay attention to not get killed.