Suggested by Vent_Hikari
First of all I've never played through any of the Kanto games so I don't really know how good it is for the gyms. So my opinion here is about the Pokémon itself.
Design wise Charizard is a pretty awesome Pokémon. It's the original fire breathing dragon they give to ten year olds so I think that's pretty cool. Mega evolved the Y version is pretty bad though.
Move wise it's pretty good too. I picked Charizard the first time I went through X and I raised it to level 100. (It was my exp farming Pokémon to evolve others for the Pokédex) Heat wave is great.
The thing is though, it's pretty overrated. By pretty, I mean very. As good as it is, there's other fire types that in my opinion are better but don't get half the recognition.
Final statement: Charizard is a good and cool looking Pokémon but shown up for more than it really is.