To me, a Perfect Game is a video game that you cannot add or subtract any elements without making it worse. Lemme give you an example:
Peggle is a perfect game
Peggle is pachinko if it was skill based and didn't smell like cigarettes. Peggle is pinball for people who hate action. Peggle is Sniper Elite, Unicorn Edition. It's the absolute perfect balance between skill and luck.
I would argue that you cannot make this game better by addition OR subtraction; every piece serves its purpose. We have several sequels and spiritual sequels to point to for this. Peggle 2 and Blast are, of course, abominations. But even cool games like Peglin have less overall appeal than Peggle. I'm not even sure adding more levels would really improve it - Peggle Nights is okay but the maps are absolutely weaker than the originals.
I have several other examples (Crazy Taxi, Katamari Damacy, Super Monkey Ball) but I wanna hear yours. What are your perfect games?
Outrun
The fact that races are usually like 10 minutes long max and there's multiple paths, so you just replay it over and over, and it's possible to get really good with it. Plus the music and vibes are excellent. Subsequent Outrun super-scaler games didn't really have the same longevity.
Ace Combat 4
Just a really good translation of air combat and flight simulation into a console experience. Looks great and runs great.
Ridge Racer Type 4
Vibes and endless replay-ability. Some of the best music and menu design. Car design is excellent. Each car is subtly different, and the way you unlock them means finishing races in a certain order.
