What makes an RPG good? Replay value. The game should be replayable countless times to be good, so that each time you could take a different path and face the same tasks with different resources.

In this regard, Gold/Silver (Crystal to a lesser extent) are an absolute failure.

Look how convenient RBY was - you had all the resources in the world to make almost any Pokemon usable. Thunderbolt? It's yours right after the 3rd gym. Ice Beam? Travel to Celadon and you can get one. Need a powerful ground-type attack? Dig is available after talking to Bill. You can try out anything with sufficient success, and you can replay the game countless times to try all sorts of things.

Then we have the disaster that is GSC, where only like half a dozen are good. The special split makes guys like Hypno and Tentacruel barely worth using anymore. And what the special split doesn't achieve, horrible movepools and lack of TMs greatly help. Most decent Pokemon need to wait until, like, lv. 50 to learn a great move, if they even learn it.

The problem of lacklustre movepools is generally resolved with the help of TMs. You have Surf, Shadow Ball, a really watered down Dig and... Oh hey, that's about it. Your replacement for good first gen TMs like Psychic and Rock Slide are now the Goldenrod shop TMs - the three elemental punches and Headbutt, which are way weaker than what you had at your disposal in generation 1.

If something doesn't have the anatomy to use punches (bye bye Haunter, you're now useless), it's as good as worthless.

Some may say that you can still use anything because stats make Pokemon good, not moves, for in-game purposes. Well, enjoy using Growlithe, Shellder and Weepinbell whom you can't even evolve until you beat the elite four Champion. Those are some hot stats right there.