I have yet to have "bad sex". Even when it was "just ok" it was great! Even when it's awkward, you'll think to yourself, "That was really awkward, oh well, we'll just have to do it again. Practice makes perfect."
It helps to really like the person you are with, but it's really not a prerequisite. In fact, not knowing the person may help make it better cause the two of you can just go at it without the pressure that comes along with having sex with some one you have to see the next day.