In the Low Quality review queue a single Looks Good click is enough to take the post out of the queue, I believe. I'm basing this on empirical observations but on Stack Overflow at least, this appears to be the case1.
The system should not be quite so simple as it enables a single mis-click or robo-reviewer to stop spam/non-answers from being deleted and allows a single "looks good" to override multiple people's delete votes. I had envisaged this more as a scoring system; say the post has to reach a score of -X to be deleted or +Y to be saved. A Recommend Deletion click would be a -1 and a Looks Good click would be a +1.
If Y is less than X then a minority of people can still save an answer from deletion by people not paying attention but they cannot overrule the majority easily. If, for instance, Y was 2 and X was 5, once 4 deletion "votes" had been gained it would take 6 looks good "votes" to save the answer. Equally, the one person who clicked Looks Good at the beginning cannot take the post out of the queue on their own and if an additional 6 people think the post should be deleted then it will be. (Obviously, these numbers are not necessarily appropriate for every/any site in the network).