What actually happened between Romero and Carmack ?

From my understanding the reason why Doom and Quake were so successful was because of the dynamic duo that Carmack and Romero were. Romero made sure the game was fun and addictive Carmack made sure, everything was technically proficient. Romero without Carmack you get Daikatana, Carmack without Romero you get........Id without Romero

I remember hearing there was a falling out between the two at one point, what was it ?

I have no doubt that they've patched things up by now, so what's stopping them from collaborating again ?

Do you think the two could bring the magic to the FPS, genre again ?

Is anyone slightly curious/ worried about Doom 4 gameplay ?

Carmack left id for Oculus which a good thing. He hasn't done anything really special since Doom 3. Megatextures in Rage are nice and all, but when both Rage and the new Wolfenstein have a 60fps cap on pc, you know something isn't right.

There isn't any gameplay footage of Doom 4, so I don't have any real expectations.

It was something about Romero having his own ideas for for Quake, he wanted it to be focused around melee weapons or something and got all pissy because Carmack and the rest of the team didnt want that so Romero got the titty lip on and started slacking off a bit leaving everyone else to do most of the work. After Quake was finished he was forced to resign and went on to make Daikatana which did have melee combat in it.

Borrow "Masters of Doom" from your library. It's the story of how they got together, what happened, and how they ended up.

Basically, Romero was the designer/idea/story-guy, and Carmack was the brains/engine-programmer. Success got to Romero's head more and thus his ego swelled more. They both went separate directions to develop the game they thought would work best next. Romero (Daikatana) focused more on design, with big ideas, huge time-spanning story, etc. and had technical issues and delays due to jumping from using the Quake engine to the Quake II engine which while looking better turned out to be more difficult to transition their code to than previously-thought, a new un-proven team, and a horribly misjudged timeline for development. Ultimately, the game demoed poorly with little content and bad performance at E3. Carmack focused more on the same formula but with better and updated technology and showed off Quake II running well. Because this was at a time when hardware was still expensive and new flash-bang-whoos-aahs were amazing and trumped new ideas (still happening today?), and because of the distaste left in people's mouths as a result of Romero's monster ego and behavior, Carmack's idea did well and Romero's tanked.