It adds in a HUGE number of new creepers, each unique and dangerous in its own way. Some notable examples include:
The fire creeper, who loves lava and spits out fire when he explodes.
The dark creeper, someone you don’t want to run into after the sun sets.
And many many more! The complete list of creeper types is as follows: Fire, water, electric, earth, reverse, snow, light, dark, cookie, illusion, magma, psychic, spider, stone, wind, ender, solar, hydrogen, EU (requires IC2), and flux (requires a mod that uses redstone flux).