I totally agree, I had a similar experience at LHR when I arrived on a BA flight from Delhi recently.
The aircraft couldn't pull onto stand due to a defective airbridge, so we had to deplane and use a cement-floored staircase, which some pax had difficulty in negotiating. I know this kind of problem happens at other airports, but over the years I've used LHR many times and problems with airbridges or aircraft parking seem to happen more frequently at LHR. The terminals are definitely showing their age (roll on the T5 opening!) and yes, the toilets are often filthy. Why does BAA love acres of swirly patterned carpet so much? It looks so dated and an eyesore. The signage is appalling, and of course, assumes everyone understands English.
One of my main gripes has always been the bus stations.The T4 bus station has no departure information such as monitor screens, which means bus pax end up asking their equally bemused travellers about which bus leaves from which stop. The central bus station, amazingly, also has no system of monitors near the bus stops with departure information, although departure information is posted on a board in the booking hall. In my experience, drivers and supervisors can be relied on to be over-officious and unsympathetic in their dealings with travellers. And yet we are constantly exorted to use public transport to travel to/from the airport.
Despite this, some airlines do go the extra mile to give very good service at check-in. Full marks to Virgin Atlantic, United, Air-India amongst others. Nil points to BAA though.