Well, first mandatory boss. :p
Yeah, some people beat him first try. And congrats to those who did.
But his speed and aggression, combined with the fact that you can barely level yet (or can't level at all, if you missed Cleric Beast entirely), means that you have very little room to breathe. He punishes panic mashing and panic healing, both of which are concepts that are taught to you more slowly in Souls games. Father G hits you with all of those things at once, and it's very rough for a newcomer to catch on to all of these things right off the bat. That's why he can be very hard to beat, and is often where a lot of people put down the game.
Like you said, if you can parry reliably then he can be beaten that way. But if you don't (and people typically aren't comfortable with that mechanic so early in the game) then he is definitely way harder than what you'd expect from one of the first bosses you see.
Later bosses may be stronger, but by then you're more familiar with your weapon, the game's mechanics, your build, and so on.