I don't think we had state by state polling back then, but the consensus was that Reagan would win by 2-4 points nationally, so his landslide win was a shocker.
Reagan 1980: 50.7%
Obama 2012: 51.1%
The EC is a deceptive representation of what happened in that election.
Carter got 41% while Romney got 47.2% and Anderson at most got 60% of Carter voters while at least 40% them would have voted for Reagan.
Reagan win by basically 10 points is still a landslide
Nobody disputes it's a landslide. Some people, however, such as myself, dispute that the extent of the landslide is greatly exaggerated due to the extent of the EC. When there were bigger defeats of incumbents. Taft lost by 19 in the popular vote and Hoover lost by 17. I also think that due to the closeness of several southern states, it is important to state that the election was indeed closer than it looks on paper. Still a clear Reagan victory, but not the historic blowout that the map makes it look to be