I'm calling these 'least favourite' rather than 'worst of' because they are plays I didn't like or didn't get on with for various reasons and that doesn't necessarily mean they were bad. It looks like the National Theatre hasn't had a good year but I saw so much there it's probably proportionate. Probably.
So in no particular order:
Hard Problem, National Theatre - Eagerly awaited and subsequently disappointing new Tom Stoppard play, it just wasn't engaging enough.
The Mentalists, Wyndhams - From Richard Bean I was expecting One Man, Two Guvnors belly laughs instead I got mild amusement.
Game, Almeida Theatre - Underwhelmed by Mike Bartlett's exploration of a topic that has been covered better elsewhere.
An Evening At The Talk House, National Theatre - Felt very long for a shortish play which speaks volumes
Waste, National Theatre - Lack of shock value made this a dull political piece