The major issue for me is aesthetucs- Not having a button to go to the next page, and forcing the bland "Previous/Next Chapter" empty space at the very bottom of everything is just so horribly ugly...
However, another (admittedly more slight) problem is that it IS a slower load than Legacy. I don't feel like there's a viable solution to that problem- But an option to at least retain some of the aesthetics of the legacy reader would be nice. Simplicity is much better than the horrid, newfangled Futuristic look the current reader is going for.