For me, it was Gottlieb Neptune. I picked one up due to the unique look of the scoring reels. The game was fine and fun, but did not really grab me until the scoring was changed to Novelty mode.
That one change completely altered my perception of the game. It is now my #1 favorite EM. Three balls and WOW set to 50K points plus machine gun knockers equal an incredibly addictive game. The game requires touch, sharp shooting and nudging skills.
Another machine that caught me by surprise was A-Go-Go. The spinning roulette wheel between the two sets of 2" flippers coupled with the simple design of three pop bumpers and a ball capture, makes this game incredibly entertaining. If I find another one for a good price, I would definitely add it back into the collection.
Marcus