( I'm aware that some years ago Glenn Close played this same role on the stage to great acclaim.)
Okay, I can take the conceit and look beyond that. But it requires a mighty heave of acceptance to find that early in the film she meets another 'woman' doing exactly the same thing (small world!) with whom she has to share a room in the hotel in which s/he works as butler-cum-waiter.
That's all I'll say about the plot. But I would have expected most of the tension to have arisen from the situation of the Mr Nobbs character trying to avoid discovery of her true identity. I found very little suspense in this direction, though that may have just been me sitting in an almost empty cinema while the hot sun was blazing down outside.
To be fair, the film did pick up a bit in the final 20 minutes or so. There is a short scene when both 'Mr Nobbs' and the other female/male character (played in full super-butch mode - though I didn't find her male portrayal very convincing either) put on proper women's dresses - and, curiously, they look much more like men in drag than they did as men when wearing men's clothes.
Didn't care either for the facile 'tying-up-the-loose-ends' final scene which was too predictable and easy.
Overall, then, a disappointment for me. Feel it ought to have been better - and maybe it was so when live on stage.
My score for 'Mr Nobbs'..................4/10.