I used Luton today, for the first time in several years, and my experience was quite different to that of the contributor who started this thread. I found it spacious, clean, efficient and (almost) a pleasure to use.
Even at 5.30am, all the shops and food outlets were open and fully-stocked, with sufficient staff to deal with the number of customers wishing to use them (which is more than I can say about the Eurostar terminal at St Pancras, for example), and everyone we dealt with was courteous and efficient. Almost every security channel was open and there were no more than half a dozen people queuing at each one - I've frequently waited longer at security at London City than we did at Luton today. On the way back this evening, all the immigration desks were manned and we were through in under 30 seconds.
Luton is clearly a low-cost airport, with some fairly basic construction and fixtures, and additional charges levied for everything from dropping-off passengers to plastic bags for your liquids to fast-track security. But it is very far indeed from being a "third world" airport.