I started this game about a week ago, admittedly I haven't had a lot of time to play it, but I'm yet to beat the first boss (always get killed by the crystal salamander as well).
In Bloodborne, the first two bosses were very challenging for me as well, but I think because you start out in a much more open area in BB it was much less frustrating because I had a lot of fun just fighting regular enemies, learning the mechanics etc but in DS3 it starts out in what feels like quite a small area with nothing but the basic enemies, one tougher one and a boss.
I've always sucked a bit at these games, Bloodborne is the only one I made considerable progress in (guessing I'm about 40-50% through BB and around level 40). I love both Demon's Souls and Dark Souls 1 but am still in the relative beginning of those despite having about 4-5 hours playtime on them both, but my lack of progression in DS3 is on a whole new level...
The game seems awesome from what little I've experienced of it... but I'm kind of thinking maybe I should start over since I'm basically at the very start anyway, I thought Mercenary would be a decent class to choose but it's probably more about me not being able to git gud enough to beat the first muhfuckin boss in the game.
I've watched a couple of youtube videos to help have a better idea on how to approach the fight, and taken their tips on board but still often die even before he transforms to his second form, and once he does that I rarely get more than a few hits in before he merks me.
One upside is that for lack of other things to do, I've practised parrying a fair bit (something I neglected to really learn in older Souls games) and though I still only pull it off roughly 20% of the time... it's better than 0% I suppose.