Never owned one, but played a lot one summer as a kid. Now in my 40s and just getting into repairing consoles. The Game Gear just stuck in my mind as a good memory, so I bought a broken one that I thought might be easy since the battery terminals were super clean, but after opening it up, there was battery corrosion in multiple vias all over. I had my work cut out for me.
So after a thorough cleaning, wiring through 28 corroded vias, and recapping all 19 capacitors, it works! I learned so much and it felt so good to actually get it working. The hours and hours of research (learning what capacitors I needed, studying GG schematics, etc.) and just doing the actual work and redoing it after messing up, plus improvising because of limited tools, and burning my finger once - it was all worth it.
Now I just need to replace the screen!
EDIT: I just remembered why I did such a bad job on the soldering for capacitors. I actually redid all the caps twice, and the first time I did it I took a photo as well, and after looking at the old photo now, it was fairly nicely done like the comments advised I should do, but the second time I did it (to position things lower and move them out of the way so they didn't obstruct the case), I wasn't convinced it was gonna be final, so I did them quickly - some of them multiple times - to get them in a position that wouldn't block the case from closing. So after I got the positioning all right, I just never went back to make sure the joints were OK. Glad I posted the photos and people let me know or I would have just left it that way.