Amy's interaction with Sheldon was great, and the way they both treated their group as guinea pigs for their experiment was nice and actually made me think about how we can easily be manipulated with rumours. I like that sort of piercing humour that makes you both laugh and think - the opening scene also lampshades the ridiculous lengths some people go to 'dumb down' science. I agree with Sheldon there - there's a famous anecdote about Einstein re-explaining relativity to a party guest who kept asking for a simple way to word it, until he finally understood but, in Einstein's words, 'it was no longer relativity theory.'
Leonard was nice too, a supporting role (as it should've been from the outset, IMO) and the bathroom scene is a nice way to prepare the audience for the upcoming episode, which begins with another bathroom scene. Nice continuity with Raj's crush, and interesting sibling scene - nice to see they genuinely love each other and how she teases him and gently hits him ... realistic again, and one of the reasons why I wanna see Leonard's siblings at some point as well as more 'Shelly & Missy'. Not everything on TV has to be soapy love triangles and friends acting with hypocrisy.
All in all I liked the way some storylines are connected with previous or later events - the smoking monkey, Sheldon's rules, Raj and Bernie, grasshopper, Penny's double standards (it's OK for her to gossip, but not for Leonard's girlfriend). It seems that the writers have been watching more Community and less Two and a Half Men.