This game had the "Dark Souls effect" on me: I hated my first approach to it. Beat a couple of bosses and then abandoned to never play it again 'cause it was so unfun... ...But when I engaged on a mission to finish every single game I started, I had to face it again, and I was so unhappy with the sole idea.

After a fresh start I played for two unpleasant hours and quit again until the next day. Then I came back and something started to snap. I started to see a "Megamanish" relation with every boss phase and every weapon (shot) you can get. From that point I felt more engaged with the game, and started to try a lot of different things. It started to look a little more strategic than pure random bullet madness. And every time I was exhausted, I just stopped, gave me a break, come back to it the next day, and bosses that were impossible at first, I managed to beat them in my first or second try.
It was nuts.
And with that I started to comprehend the rewarding felling the game gives you in so small doses. I started to worry less about how to defeat the boss, and spend more time appreciating the music, the art style, the ideas from which the developers took inspiration, and the whole package on itself. All of this elements are phenomenal, no doubt about it.

Finishing the base game was my objective in the beginning. In the end, I beat even the DLC and wanted to see more.

It takes a while to understand why this game is so popular and loved, and is not a game for everyone by any means, but once you get there, is a masterpiece.