IIRC Ai Senshi Niiol is a Disk System title, so that got me to thinking of more FDS-specific stuff. Obviously you might wanna go the Japanese SMB2j/Lost Levels or Doki Doki Panic, and if you can find a cheap copy All Night Nippon Super Mario Bros.
Checking out stuff like Zelda 2 and Dracula 2 is also fun to note differences on. I got an FDS with a cheap lot of games, but I have not got around to checking out some of the other stuff. The Twinbee game should be fun though... I unfortunately do not have a copy of Nazo no Murasamejo yet.
As for cart games, I believe Splatterhouse: Wanpaku Grafitti and Akumajou Special: Boku Dracula-kun tend to get recommended a lot too. Can't remember much else at the moment though..