I mean... I think being popular is a pre-requisite in order for something to be overrated. Mewtwo is popular, but he isn't overrated because he's legitimately quite unique in design/concept/origin. Charizard, on the other hand, is a fire-breathing dragon. How many fire breathing dragons exist in fiction? Oh, his tail has a flame on it? Revolutionary.
If you want to compare to his starter counterparts, a turtle with water pumps on its shoulders is a lot more creative. A plant/dinosaur hybrid capable of photosynthesis is quite unique. I guess they don't possess the mass appeal of a fire breathing dragon, though, which kind of goes back to my point.
In any case, I'm in the JP region, and I voted Green. Red was my OG Pokemon game and the love of my life, but Venusaur will always be my baby.