I liked most of Mountain King Studios' games, in particular Raptor: Call of the Shadows, and DemonStar Secret Missions 1 and 2. For all of those what drew me in most of all was the level of detail put into the levels, Raptor especially so. Never a dull moment in the background, each level was unique and always had different landscapes and buildings scrolling by, many of which you could destroy. In Raptor I also liked the progression of the stages where you started out in what looked like some sort of desert/barren part of the globe with ramshackle buildings and no clear color scheme amongst enemies, so it looked like you were fighting a haphazard group of mercenaries. Then you'd move on to greener, built up areas where enemies' paint themes were more uniform, giving the impression that you were now fighting an organized military. For the last stage you'd be switching between planets and moon bases which each tended to have their own theme.
DemonStar SM1 and 2 had prerendered graphics which looked really pretty, though the backgrounds tended to be a lot sparser and there was less enemy variety. It was a lot more arcadey: there were fewer levels overall and no option to save, nor an upgrade shop, instead you had to grab various powerups during the game, which in some ways added the tiniest bit of depth to the gameplay.