Donkey Kong

And with this, platformers have become a thing, and Mario heralds it.

This game is also incredibly merciless on MAME. Play the MAME Japanese version! It always features all four stages in a cycle. The NES port is way easier, plus the arcade version adds in a level to spice things up a bit. It's really interesting how many standard platformer tropes has this game brought, from the casual use of ladders and platforms to jumping inbetween those, enemies with different patterns and power ups you need to use skillfully. Fantastic gameplay mechanics that still feel fresh to this day.

Atari 2600 port's profound blockiness makes its Donkey Kong far easier to categorise, and also disfunctional. Only two levels, too, the second of which feels like a laundry-list task with the flame monsters being incapable of climbing ladders. Colecovision is sweet and worthwhile if you can't play the NES port. The ZX Spectrum version is a coding wonder and a fairly competent rendition of the game that's worth playing, and it was probably how a lot of UK kids were first exposed to Mario. A real stunner has to be the Atari 800 port, which even further randomises barrel placement and also picks up the pace, it's a very unique port that makes the game feel different. It also retains all four levels!

The Intellivision one is pretty bad.