To this day, I've yet to see a UE4 game that I could run without lag.
Judging from your documents, it would appear that you managed the main things you set out to do. However, I noticed your design plans seemed to be just how the game should look and the broadest progression. Is that normal for formal planning? I would've expected more details along the lines of how high the pixel could jump as a multiple of their own size or at least what sort of control scheme to use.
Regarding the game itself, I noticed a couple pixels that needed to be 3d to get but that I couldn't reach due to being still 2d. It made sense after the switch, but in the moment it seemed like a bug, especially since there was no indication of how to progress.