Let's see,
The 2nd Doctor, Jamie and Victoria have to stop the Great Inteligence who has tricked a human into making killer Abominable Snowmen.
The 11th Doctor and Clara in Victorian England, have to stop the Great Inteligence who has tricked a human into making killer Snowmen.
Then...
The Great Intelligence returns and tries to drain the 2nd Doctor's mind with technology, Robot yeti run around grabbing people.
The Great Intelligence returns and is draining human minds with technology, Robot spoonheads run around grabbing people minds.
The 11th Doctor has to stop this World Wide Web of Fear.
...and
The 2nd Doctor Jamie and Victoria land at a Research base covered in ice.
The scientists have found a creature fozen in a block of Ice and it gets thawed out. Ice Warrior takes Victoria hostage and tries to take over or destroy the earth. Doctor has to stop a nuclear explosion.
The 11th Doctor and Clara land on a Russian sub, under the ice.
The scientist has found a creature fozen in a block of Ice and it gets thawed out. Ice Warrior takes Clara hostage and tries to destroy the earth. Doctor has to stop a nuclear disaster.
It's no wonder people say they see so much of the Second Doctor in Matt Smith.