Me? Well I guess you'll all think I'm a little nuts, but here's my absolute all time number one beats everything favourite thing about this game (which is not to say that I don't pretty much agree with everything positive that's been said so far)....
I love that it takes so damn long to get anywhere of real distance. I'm currently thousands of light years from the bubble. So somebody might ask "hey, you coming to look at <something>?" My reply? "Sure, I'll be there in about a week/month/whatever". Okay, so it's not real and the speeds are actually way too fast, but nothing, NOTHING makes me feel like I'm out in the vastness of space more than the sheer time involved in going anywhere at all.
Note to Devs: please don't ever put in fast-travel. At all.
Hear hear, far too many people calling for faster travel ... I pray to god Frontier never listen to them. I'll never forget Buckyballing to Sag A and then realising that, at my normal rate of play, it would be months before I got back home again. I found the prospect both horrifying and thrilling.