Alice Cooper's Nightmare Castle
I've been playing pinball for a decade and this game has made me better than any other game on the planet. Orbits are tight, controlling the ball is difficult, ramps are down the middle if you don't hit them correctly, etc. I went from an average player to one that wins big(ger) tournaments, and it's all thanks to this game.
Another good one I think is TMNT. I don't love the game itself -- borderline hate it -- but if you can hit all the shots in this game, stage the flippers to get the jackpots and loops, then you can dominate many games on the market.