I had my first trip on an LS 757 the other week, and to be honest it wasn't bad!
Aircraft was G-LSAC out and back, the new seats are a bit hard for a long sector but otherwise everything was working and the aircraft wasn't in bad shape at all. A very enjoyable trip and the LS cabin crews are some of the hardest grafters I've seen, so if any are reading this well done to you. The only issues I had with the aircraft were smelly toilets which really do need a bit of a steam blasting.
I can see the point of the new lightweight frame seating though, it must save a lot of weight and therefore fuel. Over three hours and backache sets in, but for an average lowcost type sector they are perfectly adequate and look very easy to maintain. It will be interesting to see how a few years in service daily affects them but the red leather facing seems to be robust enough and looks like it can be changed on the line without major surgery.