I didn't love everything on it (for instance the 'plot twist' near the end was too predictable and it's sad to think that we may not see Raj's sister again) but the Halloween theme was excellent and though I usually don't enjoy it too much when Sheldon's ridiculed, it was nice to see him getting pwned and facing (though most likely not learning) the Aesop of 'sometimes thorough scientific thinking isn't enough.'
If I sat here and overanalysed it I'd probably find myself making annoying complaintsabout character undevelopment, Flanderisation, etc., but if I keep myself from doing it and enjoy the episode as what it is (entertainment), then I realise it's very well-done and well-written.
I wonder if Penny's plot will affect the canon at some point (i.e. if there's something deeper going on). That'd be nice.