Not that bad of an ending. They probably could've still used a few more chapters to develop the relationship of the brothers and their friends. Although I'm pretty satisfied with the reveal behind the truth of the time warp and Megumi's character motivations.
Still, there's a few things that bother me. I think they shouldn't have gone back to the original timeline if the future there was also changed. They might as well have stayed in the new timeline since the results are practically the same with the five of them being friends. Going back to the point of their graduation did make the friends as well, but also caused the three of them to skip a couple of years worth of memories and experiences. Basically, it was convoluted and pretty unnecessary.