I'm not being funny but the biggest difference I've found on the LCCs are the clientele! Wiith BA you don't often hear the crew having to tell passengers to 'calm down' on the PA system! (unlike my last Ryanair flight)

Other than that, now that BA has lowered its standard, there really isn't much difference at all. OK they still serve complimentary snacks and drinks, but the savings made on LCC bookings mean that you can buy on board and still be quids in. The seats are much the same.