I have two recommendations:
first is Dragon Crystal, which is featured on both Game Gear and Master System. BUT. there is only one song that plays throughout the whole game, and if I recall correctly, the song for the game gear version is far superior.
this is an early roguelike/mystery dungeon style game and it is quite engaging. you are constantly finding new equipment, and much of it requires you to wear it in order to identify it, which can cause you to equip cursed items which can’t be removed without using a certain scroll.
it’s quite an enjoyable game, although towards the later levels it becomes a bit tedious because to advance you must press a button while facing certain walls, and rarely the walls will be destroyed as fake walls, and this is a big pain in the ass.
the second recommendation is Soltaire FunPak.
now you must note that there are at least 2 solitaire games for the game gear, and the other one sucks - “Poker Face Paul’s Solitaire”. I’m sure everyone here hates solitaire but I find it quite enjoyable and when I had the Odroid Go basically the only thing I played on it was GG Solitaire FunPak. the controls are nice and fluid, you can really get into a groove, and it’s a WHOLE lot of fun, folks. note that I only ever played the base, simple, first game, which I think is Klondike. I never learned the other variations, although they are probably great and I think solitaire is way undervalued by the gaming community.
note that to inject genuine fun into the game, you must place limitations. if you have unlimited cycling of the deck and only 1 card movement, then the game is not a game at all but simply just going through the motions. however, if you only permit 1 cycling of the deck, and 3 card movement, then it is genuinely challenging, and you must think and plan and perhaps use undoes.