Yeah, it's not that hard compared to later games, although I've only done DS1 and 2.
They're really pushovers compared to the shit From cooked up in later games.
Basically. Flamelurker and maybe King Allant are the most later-souls-game-like bosses this one has. Then again, the heals in this are a big part of the reason why it's not that hard, little chance I would have done King Allant first try without this game's liberal heals. Maybe I would have, maybe I would have just played in an entirely different, safer way instead, who knows. In a sense it's not that bad of a thing to have more heals since the alternative will mean players just rat, cheese and spamroll harder.
Dragon God because I completely forgot the set of "puzzles" you gotta do to beat him.
Yeah, he's dogshit. As I said, Bed of Chaos of DeS.
I'm 90% sure that the way you're supposed to stand behind the pillars down the stairs is fucked up too. I made this top-down diagram of what I mean. Even if the dragon has clear line of sight if you're standing directly behind the pillar, he can't hit you there. If you stand in the crossed off area where he can't see you, you get hit by fire somehow.
As for playtime, DeS took me about 23.5h, give or take. I don't have numbers for DS1 since I pirated it, but DS2 took me 44 hours with all DLCs.