I think the best part is the execution. I know it's a very vague/general thing to say, but that's what it boils down to. I can't point to any single thing in the game and say "that's the best part!", instead the game is full of stuff that does what it's supposed to and together, contribute to making it awesome. No single thing is perfect, I don't agree with every design choice but they do form a very streamlined, slick game.
The worst part, I think, is the closeness of the maximum zoom level. I so wish it were possible to zoom out just a little bit more, even one or two more steps. I've been told it isn't happening and I can accept that, but that continues to be the thing about the game that I most wish could be changed.
Yeah zooming is quite a biatch, I'd like it to be slightly further for the bigger ships to help you see more around it. Someone could make a mod that changes this I guess
Best feature is the sound effects.
Worst is the tactical display user interface and control scheme.
The tactical display will likely be improved over time. I'm sure I've seen Alex mention something about this somewhere but not entire sure lol