I was mulling this over, trying to find any common elements in my faves. Not in any particular order, I like ancient (not necessarily the Ancients) mysteries as in "Raiders of the Lost Ark", "Forbidden Planet", "Twilight's Peak", and the "Sky Raiders" trilogy. I tend to prefer small-unit or non-military action, probably because I don't have a military background, and tend to get details, tactics and strategy embarrassingly wrong. However, I tend to run bad guys as arrogant, over-confident space martinets, so it doesn't hurt too much if they have the military sense of Steve Urkel. I like there to be something alien or off, even if it's just a green sky, or calling a horse a smeerp. Most of my players don't have a strong science background. I may have the most knowledge there, somewhat coreward of Discover magazine, but somewhere rimward of Scientific American. Ergo, not a lot of real science, or even technobabble. I guess to slap a single label on it, low rent space opera, more toward the "Firefly" end of the scale than "Star Wars".
I also tend to use the word "tend".