What's wrong with the weapon handling and general feel? I can't say as I see anywhere specifically that these could be improved, apart from reworking the UI a bit to make it easier to navigate.

I think having Mac and Linux (which it already has) support is important, it expands the potential player-base and would be/is nice for those of use who don't usually use Windows (or don't bother with it at all). But I do agree that it probably isn't as worthwhile as other things, in the end though whatever seems the most fun to work on will be what gets done first at this point I imagine.