The game can be fun with its different mechanics and whacky glitches, but a lot of Pokemon are awkward to use, the AI is basically braindead, the region isn't hugely interesting, the colour palette is limited even on a GBC and there's literally no postgame and no way to really get high in levels. Also Yellow was finished before the anime series had even reached the league, so it could've done so much more with its adaption, but it just fizzles out after the 3rd gym.
Like with Gen 2 the games can be fun, since Pokemon hasn't changed much, but man the limited movepools and lack of mechanics and tedious gameplay (a lot of routes are just stuffed with weak trainers for no real reason other to inflate the level curve) means they're pretty hard to go back to. Playing later games is just so much smoother and more enjoyable for me. Sometimes playing the older games just puts me on autopilot.