They each have an objecive. Plant the bomb, rescue the CSGO Sale, and an unmentioned objective, get the VIP where he needs to go. Iceworld has no such objectives. It is a small map and looks very much like a pound(#) symbol from overhead.

 

A buy zone is located in it's center and T's and CT's spawn across the map from each other. With no objectives the goal is total annihilation. Kill all of the opposing force before they kill you.

 

Environmentally, every wall can be shot through if you have the right gun. When you run around the map you can hear your footsteps, or someone else's, in the snow. The sound of heavy fire from all sides is all around you from the start, and often to the CS GO Skins free.