I've only killed 6-7 bosses, so far the only ones I haven't killed first try was The Pursuer and the 3 Alien dudes. And I'm terrible at Dark Souls, I find the mobs leading up to the bosses way harder than the bosses themselves.
Not very far so far, I started out wanting to play something different. SO started playing a Sorcorer/Hexxer/Zeus, but really didn't enjoying playing a caster. Got to just after No-Man's Warf before deciding to start over again, as a strength dude. I'm finding the game a little more difficult that Dark Souls 1, so I'm playing much more conservatively than I usually do. On my Warrior, rocking a Bastard Sword +4, I'm just past the Giant dude in the Forest of Giants.