I have to admit, when this character first appeared in SG-1, alongside Amanda Tapping and the rest of the cast, I didn't like him at all. He was annoying and challenged Sam Carter (Tapping), not just intellectually but morally too. He bugged me because what he said was plausible and there stood a chance that he would be right and Carter would be wrong. After a few episodes of disliking him intently, he made the transition from reoccurring SG-1 character, to Stargate Atlantis (SGA) regular.
The Rodney McKay of SG-1 was a pain in the neck, but the Rodney of SGA is brilliantly quirky. David Hewlett plays this character extremely well. He (Rodney) not only entertains the audience but the rest of the cast too. He's a hypochondriac, annoyingly smart, arrogant and awful with women, but his quirky-squirmishness sets a scene of comedy, where many sci-fi shows can be seen as perhaps stiff and dry. He is by far the funniest character of the show and that makes him very entertaining to watch. Who said techno babble was boring, not I.