I saw The Frogs the other day. Great fun, very fringy, weirdly hetero considering how camp it is, but the second act drags like anything. If they'd cut it down to a tight 80 minutes straight through it would be perfection.
My Master Builder is almost certainly the worst play of the year. It's absolutely shameful that a play that dire, by a first time writer, went straight into the West End just because the playwright is an ultra-wealthy and well-connected socialite who is best friends with many powerful celebrities. One of the cast is married to a friend and I heard the cast accepted based on Michael Grandage + 3 month West End run, without seeing the finished script, and are now mortified with having to perform such poor material. Lots of lines that are clearly intended to be deadly serious meditations on art and live generating giggles, or even howls of laughter. It's almost Mystery Science Theatre 3000 territory it's so bad.