For me, it's the lack of mobile view. I like this place, more than any website I use (and I use a lot) but having to zoom in and out and move the screen with the text to read is just as painful as nails on chalkboard. I'm very surprised that this website doesn't have mobile view. Its the only website I know that doesn't. Considering how big it is...it's crazy.
My mobile maybe too small to login into the forum but I don't really see that as a challenge , I try to be always active because I learn new things about in the forum every day