Well, I'd like to make it clear that I'm not out to disparage the current PB2 client (because it's
very kind of you to provide a standalone client).
Since you asked, though, I'll tell you what I like about Q2E that might apply to future versions of stand-alone PB2:
1 Rendering is on par with, if not better than Quake 3's. This includes optional shadows, dynamic lighting, quality particle effects creating colored smoke, et cetera. Vanilla Quake 2, while a far superior game to Q3 in terms of play, IMO, looks pretty dated in comparison. Played in Q2E's engine, though, Quake 2 and its mods look eye-popping-ly good.
2 The graphics are extremely scaleable via the in-game menu, keeping it slower-machine friendly for those who need fewer bells and whistles.
3 The Q3-style handling of crosshairs. You can choose from a large range and customize your size.
4 The Q3-style handling of memory. I'm spoiled to being able to allocate hunkmegs, zonemegs, et cetera.
One other thing that might be cool, though it's not in Q2E (it's from Q2Max), is an option to engage cell shading. I wouldn't make it standard, but it'd rock to be able to make it all look cartoony, if/when the whim arose.