I mean there is only one type of ammo for each weapon.
In the first game, you could use different ammo.
EG: The tranquiliser gun had "normal" darts, or tranq darts etc.
EDIT: My problem with the boss fights is not the difficulty, I've beaten them all on the hardest setting.
It's being forced to kill, as my first playthrough was a pacifist, where I didn't kill anyone or set off any alarms or enemies firing.
Being forced to fight and kill them didn't fit with being a pacifist.
Ahh, I see what you mean now by the ammo types. Yeah, that was a bit of a wasted opportunity, I guess. Still, there's enough diversity in the ways to take out enemies in DXHR that I didn't miss them all that much.
I also see what you mean regarding the discrepancy with a Pacifist playthrough and the boss fights. In my opinion though, it's being a total pacifist that feels odd. Here you have enemies who've brutally gunned down your friends, your colleagues and your girlfriend, and you're STILL going out of your way to not kill them? It just feels too unrealistic to me. (That won't stop me from trying for the Pacifist achievement, of course.) It's unlike the situation in DX1, where Paul Denton openly chides you for being bloodthirsty, and you're reminded several times by people that you're a cop, first and foremost.
I'm not saying that players who want to take a total Pacifist route are "silly", of course, but I'm just saying that it doesn't seem to stack up in a roleplaying sense considering Adam's motivations.