It seems a little hyperbolic, you're tempted to say. I think some other ones like the first time George Washington was elected in 1789, and Lincoln's victory in 1861 along with FDR's in 1932 were more important. However, I agree with Sharon Day: this is a very important election:
Sharon Day, co-chair of the Republican National Committee, told delegates gathered here Tuesday that the stakes in November could not be any higher.
"Every election we hear that this is the most important election of our lifetime," she said in a prepared version of her remarks distributed to reporters. "This election is more than that. It is the most important election in our nation's lifetime."
"We need to defeat president whose actions threaten our liberty," she said.
I also think I get why she and her Republcian friends feel that it's the more important ever. This is their last real chance to destroy FDR's New Deal. This is tehir last best chance. It is very important because a Romney victory means the end of Medicare, Medicaid. and the rest of the New Deal. It will be read by the GOP as the mandate to end Medicare, Medicaid and Social Security, etc.
If the President were taken down it truly would be over for this country. The GOP dream of returning to the 19th century would now be largely realized. Next, perhaps would be the end of child labor laws... No doubt the Voting Rights Act would be but a memory.