They used to be very good but not any more. They are always delayed or cancelled. Very overcrowded. I travel with them 3- 4 times a week from East Croydon to St Pancras ( return) and there's no day where service runs without delays or cancellation. Today they used excuse that engineering works weren't finished on time. Another day they said there's kids bike on the tracks!!!! Come on!!!
Also trains are extremely hot in winter months. Very uncomfortable when you are standing there with hundreds of other commuters pressed against each other like sardines. Horrible!