jungles suck, they really need to replace the ground foliage with some kind of high grass, two blocks. they also need to have a stuffload of sugar cane. also, deserts have much too many water pools.
IMO i think a mini biome thing would be nice, like the way villages and desert wells spawn in deserts, deserts should spawn oasis's . a pool of water with some normal jungle trees and grass around it instead of having a pool of water every 6 blocks. i think that could also be applied to other biomes, like jungles could have jungle shrines with some stuff in them or forests could have patches of flowers with a gift in the center.