My son thought he was an FPS expert until

[obsidianspider]

Any of the Makaimura (Ghosts N Goblins) games.

[mediamogul]

@obsidianspider

Any of those are always a challenge. Have you been able to beat 'Makaimura for WonderSwan' yet?

[reddragon1]

Load up Serious Sam on insane setting and then get out of the room.

[Drakaen391]

One game I had almost forgot about that can be hard is wizards and warriors for NES....

I love playing it with save states now....

[obsidianspider]

@mediamogul I've never beaten any Makaimura game. They're so fun, but I am awful at them.

[backstander]

Little Nemo: The Dream Master (NES) and I believe there is an arcade variant just named Nemo.

Also the original Contra (NES) without the infamous Konami Code.

Last, Mike Tyson's Punch-Out!! (NES)

Update:
Oh yeah...don't forget Super Mario Bros.: The Lost Levels (or also known as Super Mario Brothers 2 in Japan).

[mediamogul]

What's up @backstander? Good to see you around. Playing anything noteworthy at the moment?

[backstander]

Hey @mediamogul ! All this month I have been focused on completing Mafia 3 on PC 100% with all the DLCs. On my RPi, my son loves Pac-Man and Ms. Pac-Man. I'm really not very good at it but I really like the Ms. Pac-Man / Galaga combo arcade because you can just continue where you died instead of starting all over at the beginning lol.

[mediamogul]

@backstander

Your son's got great taste. I'm not all that great at the Pac-games myself. Playing 'Jr. Pac-Man' has helped a lot, as the lack of tunnels forces you to be hyper-aware of your surroundings and possible escape routes. The tactics carry over to the other games, but it's really become my favorite of the series anyway, so I usually just play that.

[Drakaen391]

One of the few I beat