Damn I thought it was awesome. The second season was disappointing though it ended well, but this was awesome through out. Very few episodes dragged... and some episodes were totally top notch. Maybe it is because I came off of the inconsistent Heroes show, but I found this to be awesome.
The ending totally caught me off guard, though I don't know how they'll manage the next few seasons.
And that Locke bit where he encounters Jacob... that really freaked me out...
Great season.
edit:
Was happy to see on wiki that it was really well received. The first six eps may have been slow, but then it was one badass episode after another. I can't wait for season 4 to finish, so I can start watching. Damn this writer's strike. Fucking great season though.