The Born Again storyline, one of my favorites, is a story that was built over time. It was the culmination of a rivalry that was built over decades. DD and Kingpin need a lot more history before anyone should be attempting it.
They could do it in a second movie and still have the same kind of impact, as movies always condense the stories. Look at the X-Men, Magneto teamed up with them in the second movie and it worked, it *did* feel like a team up of deadly lifelong foes, only after one movie of them being at odds. It felt similar to Magneto teaming up with the X-Men in Secret Wars after, literally, decades of fighting to the death.
edit: Same deal with DD and Kingpin, with these kinds of encounters, all it takes is one to make them lifelong deadly enemies.
Timewise between DD and Kingpin though, it was not decades, it was only a few years between their first meeting and Born Again. Kingpin has been around since the 60s, but he was always a Spider-man villan, he did not meet DD until Miller pit them against each other in the mid-80s, and then Born Again was published in the early 90s. Within the comic-book timeline, that would be even less time having passed, maybe just a couple of years.
I loathed Colin Farrel's Bullseye for the most part. I don't recall Bullseye being that overtly annoyingly craaaazy in the comics. Am I incorrect in that?
He was a very cold, calculating villan in the books, but he would lose his cool and get wound up when fighting DD. Because he was used to being the best, he did not like it when DD would outdo him, so he would get angry in the same egocentric way he does in the film. That was done correctly anyway.
The character was not really done wrong, but there is so much Colin Farrell in the character that Bullseye becomes Colin Farrell, it's not like an actor disapearing into a role, and making him something else, it was Colin Farrell with Bullseye's egocentric traits.
edit: but, y'know, I do like the performance, and I fear I am dissing a good take with faint praise, he *did* play the character well, Bullseye does have a very playful side, so thinking about it more, he/they did actually get the character down, it's just that BE also has his cold, calculating, quietly serious moments too, and we never saw that really.
But, it was a movie, so perhaps there just wasn't an opportunity for those kind of Bullseye scenes in the script. We could definitely get a different take, where he is cold and calculating, but still takes the piss wryly, and explodes into his playful side when he is in action, instead of being playful all the time.