If going to a show at the Barbican this is quite a good option. Very tasty but tiny portions. They recommend 2 to 3 per person. We had 6 between us and it was just enough. Perhaps if we had had a sweet it would have been better, but we are not sweet people. They bring the food out as it is ready and whisk the dishes away as soon as they can - which makes it feel a bit rushed. Ideally another time we would probably order them in twos if they would let us - then you could have a breather in between!
The staff are very helpful. They have a small bar seating area at the front where we sat and had a drink before we went in and it was very pleasant and quite comfortable. However the chairs in the restaurant itself are really hard and unforgiving. You definitely do not want to linger after you have finished!
They had quite a good wine list if this is important to you - as it is to us.
Despite the uncomfortable chairs (which I think they should really do something about!) the food is definitely good enough to make us want to return.