Im sure these have been reviewed a million times before but i am going on the assumption that no one reading this has modded much...if you have sorry!
Right! first off a small comparison more creeps is more of a fantasy mob addition adding things such as hunchbacks that summon skeletons when you feed them cake,robot's and many more
real mobs such as sharks bears fox's etc but also has quite a few good fantasy mobs :D
Both of these mods together can be a bit overwhelming unless you fiddle with the spawn amounts of the creatures although having a shit-ton of new mobs is fun for a few minutes it quickly gets boring so i would advise turning the spawn rate down quite a bit
Both these mods add A LOT to the game so is very good for people growing bored of the vanilla minecraft plenty of new things to do but doesnt stop you from playing the game :D
For more information go to the links below