Sensible Biomes attempts to fix some of the most disliked features of vanilla world generation without taking away the vanilla feel: no new structures or weird trees, but a much better arrangement of what vanilla already offers.

• 72 new biomes help transitioning between vanilla ones (instead of hard borders where everything changes in a matter of a few blocks) and adding variety to biomes that only come in 1-2 versions in vanilla
• smooth transitions between 7 different climate zones and vegetation types (instead of random "biome bubbles" made of plains turning into forests turning into plains forever until boom! desert)
• mostly flat beaches  (instead of sand climbing up hills)
• beaches, caves and mountain peaks in many different materials (instead of just sand or random stone splotches)
• larger biomes, but not as large as Large Biomes mode
• smoother terrain and less caves swiss-cheesing the surface
• no new structures or blocks, aside from bushes from different plants (why not), so you're still getting a vanilla experience

Transitions help find the biomes you're searcing for. Need a jungle? Go where vegetation gets thicker and thicker while plants change to more tropical species. Better than running in a random direction!