I don't think I've been in this situation before. I saw the third preview performance of Common, a new play, at the National Theatre on Thursday and despite great performances and production it still wasn't good. There were clusters of empty seats after the interval and it had been similar the previous night. I'd contemplated leaving myself - so did @PolyG and she's got far greater resolve that me. That isn't the situation though. The situation is I subsequently heard that Friday night's performance was cancelled to allow more time to work on the production.
First or early previews can been cancelled when productions aren't quite ready for a paying audience but to cancel a preview after a few performances is more curious and unusual.
So do I write about a play I saw that is likely to have had more than a few tweaks made to it - it had already lost 10-15 minutes off it's official running time the night we saw it. I've had arguments in the past about reviewing previews and my stance has always been that if I've paid for a ticket, then I can express my thoughts and opinions about what I've seen and experienced, whether that is on social media or this blog. I've seen enough theatre to gauge where things might naturally improve and tighten up with a few more performances.
Occasionally, there is something wrong with the play itself that no amount of previews are going to solve and if the preview of Common hadn't been cancelled I'd put it in that camp. Will one preview performance off be enough to sort it out? Perhaps. However, there is part of me that wants a record of what I saw, that is, after all, the primary reason for writing my blog. That's the dilemma.
PS edit: Given the response I've had since writing this, I decided to commit my thoughts to my blog.