Xena, if its a job you want go for it. Working at LHR is actually a lot of fun...lets put it this way.... You never know whats going to happen on any given day at LHR so it can be very interesting!!!! Also there are some great characters all around LHR who you will no doubt be working with. Dont be put off by the airport.
In March T5 opens up so most of the BA operation will transfer there freeing up space around a lot of the other terminals making things marginally more bearable . Then T2 will be demolished to create the new LHR East terminal which hopefully by 2010 will make LHR a more modern airport so things are gradually changing for the better.
I left QR for BA and although I was initially based in LGW (Great airport to work out of) I have been LHR based for 2 years and have not looked back. Also chances are if you are working for an airline, you will only ever see the inside of your report centre and rarely venture into the terminals!