I kind of like this default theme, but I guess it's not very Sphere-y and OH NO PIGGGGGG *MUNCH*Hm, that emoji plugin would be nice to have. Regarding issues: It seems to be glitchy on mobile; sometimes I have to tap things twice to get them to respond, which is kind of annoying. And the posting page gets too wide once you activate the keyboard, at least on iOS. See screenshot.
Not bad, nice layout. I definitely see the similarities to SMF. What version of SMF were you running prior? Last I knew, they were regularly updating the SMF 2.x line.
Oh, as a reminder, at some point we need syntax highlighting back, for JS at the very least.