"Yellow is such a noob game. It's basically just lets fanboys recreate Ash's team."
"Crystal is such a lazy game. It's basically a Gold & Silver rehash."
"Emerald is such a dumb game. It's basically just using the Ruby & Sapphire plots."
"Platinum is such a non-game. It's basically just a director's cut of Diamond & Pearl."
B2W2 introduced new aspects of Unova, e.g. South-West Unova, Castelia sewers, and Humilau City. It allowed you to catch non-Unova Pokemon really early on, like Azurill in the Floccesy Ranch. It gave you a new rival in Hugh, who is unique in his motivations, and doesn't scream about you being more powerful than him, giving the story another plot arc. There are 3 new gym leaders in Cheren, Roxie and Marlon. Elesa's image change is explained, and is not just solely a cosmetic change. Memory link allows you to see what happened to everyone in a period of 2 years. B2W2 shows that time actually passes, which is unique to Generation V, considering no other Generation has shown such a feature, and in the anime, Ash has been 10 for over a decade.
You can say any game was "bad". Why does Gamefreak make any game? To make money. If you don't like a game, don't buy it.