Zaxxon - Nothing had been seen like it before. The isometric scrolling effect was a new gimmick in video games, and Zaxxon raked in the quarters because of its visual appeal. I will say though, that as a game it was rather run of the mill to me.
Tempest - Though not the first vector graphics game, you have to admit that Tempest commanded your attention the first time you saw it in the arcades. You also have to admit that Tempest was an abstract gaming premise, one that had not seen before, and most likely not since.
I, Robot - 3D polygons floating in space. Who could have foreseen this? Wow. the gameplay was challenging as well. Yes, it hasn't necessarily aged well, but I was awestruck by it in mid 80's arcade land.
Dragon's Lair - Who would have envisioned actually being able to play a cartoon? Dragon's Lair delivered that, although the loading times were a drawback. For many arcade gamers, it was a dream come true.
Crystal Castles - A 3D adventure with a cute bear main character, and track ball controlled to boot. Wow! I remember this game being so popular at my arcade that there was almost a waiting line. Even so, I just loved to hang back and watch the action, it was such a visually pleasing masterpiece.
Darius - This has to be the arcade tech demo to top them all for me. Unsuspecting, I walked into Aladdin's Castle around 1985, seeing this, and my jaw nearly hit the floor. Three overlapping screen wide, a beautiful space shooter, and who could have imagined fish in space? Oh my! I still wish to this day that someone had come up with a true home port of this game, one that used three TV's side by side.
Any more that I might have missed?