First experience of flying through LTN recently - observations are my own as are my opinions so please do not bash me down if you disagree.
Terminal very old and in need of updating, security queues excessively long at lunchtime (not busiest part of day, not helped by some very stupid passengers which seemed to dominate the terminal that day!) and its a pitty you have to pay for the coach transfer link between Luton Airport and Luton Airport Parkway station.
Not the airports fault, but the train station could do with more staff on duty to help passengers I saw no-one. Train cancellations and only announcements to go by.
However no queues at passport control on return, baggage delivered promptly which makes for a refreshing change.