i used to spend hours on lunar lander......yet im still not sure why
First time I ever went into an arcade, there was a Lunar Lander machine. I remember it being really difficult and frustrating to play. Other obscure games I played there included: Tailgunner, Radarscope and Blasto.
I remember that I liked Blasto, somewhat inexplicably. I was hugely impressed by the sit-down Tailgunner machine, though I never really figured out how to play it properly. (In fact, I'm still not sure.)
One of my favorite almost-unknown games is Zektor. Apparently it's quite rare, very few of them were produced. I've never seen a real one, but I think it's a lot of fun.
I was introduced to Lady Bug and Cosmic Avenger through my ColecoVision. Cosmic Avenger was a huge favorite of mine on the CV. I only saw an actual Cosmic Avenger machine once, briefly, and didn't get a chance to play it. It's probably just as well. . . I've learned it was a lot harder than the CV version.
Addendum. . . I almost forgot to mention Quasar. Our local convenience store had a Quasar machine for several weeks, and I liked it pretty well. I was frustrated that it took so long to bring that game to MAME, it's fairly obscure.