No way could LOST be done in a single season.
However, I think it could have been trimmed a bit. Season 3 should have evolved twice as fast. I got bored with the caged encampment bit. And I agree with the others that 5 and 6 could have been combined. The building up of the "crossed lives" took too long and was also a bit too esoteric for most people. When LOST ended there were so many people in an uproar about the confused ending (it was "The Prisoner" all over again). I don't suggest that the sophistication of the story be compromised to help reduce the whining, but I think it could have been conveyed in a little more "digestible" manner that would still keep the story integrity and satisfy a lot more people.
But in the end it was all about money making, and LOST sure made quite a number of people very VERY wealthy. It sure worked for them