A very funny episode built around a simple but clever idea: what happens when Sheldon tries to replace his friends?
His attempts to assemble a new social circle are hilarious, particularly when Stuart, Kripke and Zack turn up and Sheldon discovers that being a host is rather different from being the centre of attention. The karaoke sequence is a highlight, and Stuart is particularly memorable here, bringing an unexpected bit of fun to the proceedings.
The contrast with Leonard, Howard and Raj enjoying an evening without him is equally good. They may complain endlessly about Sheldon, but they clearly miss having him around.
There is also a nice little subplot with Penny, Amy and Bernadette, adding another dimension to the episode.
8/10: Great ensemble comedy, with a particularly satisfying reminder that this group is rather difficult to replace.