Well I had a full synopsis (knew everything that was going to happen, in detail, except for Superman's death and the funeral) and got to see key scenes like the Batman/Superman fight and Martha rescue pretty early on, about 5 months before the movie came out last Fall. Out of context and on paper, it seemed great. I actually was trying to reassure a few members on here (you know who you are) that it was going to be great via PM and phone. Boy was I naive.
The first time I saw the watermarked, black and white footage of the Justice League laptop surveillance footage something felt wrong but I shrugged it off as "oh, Aquaman looks cool, these are small, harmless cameos that I'm sure are going to work in the movie". Come time for the final product, I didn't expect to be treated to the scene at random when Bruce is trying to prepare for his fight against Superman.
Before that insider info? I had doubts as soon as it was announced that Wonder Woman (in full costume) was going to be in this. I'm not going to go back and dig up my old posts, but I'm pretty sure I said something like "man, they should just focus telling a story about Superman and Batman, they're big enough for one movie as it is".
I was still optimistic going right into release though. Then those CGI leaves were falling in the logos, and kid Bruce was rising up the hole (in the cut I saw way back when, the Wayne murder/funeral/cave scenes weren't edited like they were in the film and there wasn't that shot of the kid rising, probably because it still required CGI bats). Then all the scenes felt disjointed, probably around the Africa/terrorist scene and Luthor/jolly rancher montage. I was pretty frustrated by the whole thing, then when you get to the third act and you have to endure a barrage of concepts (Superman leaving, Batman preparing, Martha hostage, Justice League set up, Wonder Woman stuff, etc. etc.) within the span of 5 minutes, I was just like "lets get this over with". I felt nothing during the Doomsday fight and was completely apathetic to Superman "dying".