*obligatory possible spoilers warning*
The film is a mess. It's poorly written, none of the supporting characters are particularly well-developed, it's SO LONG that by the time John Goodman makes his second appearance--nearly two hours after his first--I'd almost forgotten his character existed, the love story makes no sense from the beginning (why was he interested in her in the first place? just because they'd met by chance and are both broken people?), etc. There are so many ways in which the film fails that the overwhelming positive response makes no sense to me.
That said, I would rank Washington's performance as one of the top three in his career--and this comes from someone who is not a fan at all. Whizzer, I disagree with your characterization of his performance as simply "technically proficient". That is how I usually find Washington's acting to be--mannered, proficient star turns, always playing to the audience with a wink and a smile. This is one of the few times I've seen him really burrow deep into a character, and it really surprised me. Whatever the film's failings--which are many--I was blown away by Denzel.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body