I've visited Tabla a couple of times now, once at lunchtime and once in the evening, and both times my impression has been the same.
The space is light and modern, no curry house clichés here, and the service attentive (maybe a little too attentive). The highlight is the starters, which are interesting and creative. The usual yoghurt dip is replaced with a lentil one, somewhere in between sambhar and dhal. My Andhra Wada was crisp and flavoursome. On the most recent visit, my companion had the chilli paneer and was delighted with it.
Unfortunately, the mains are less exciting and closer to standard British Indian restaurant fare, The jalfrezi was lacking in perk and, while perfectly edible, was not that interesting. Given the vast range of exciting vegetarian dishes to be found throughout India, it's a shame they rarely make the menu here.
Cons: Disappointing mains, over-attentive service