I can only speak about the trains to and from Brighton Station but this season there have been no problems whatsoever. I've found the stewarding at Brighton to be superb, normally get a train within a few minutes and even on midweek games only have to let one train go before getting the next...
I use the trains to and from Brighton and find the service very good indeed. There have been notable improvements since season 1. More frequent trains and the queue management at Brighton Station pre-match is superb in my opinion.