Apart from its primary 'airport' function as an exceptionally busy GA facility it's actually got one over on Bristol Airport (twice in fact) with its IoM service.
Some years ago Eastern came off BRS-IOM not long after the GLO-IOM route began. Flybe then tried BRS-IOM for a while but that too was eventually pulled whilst all the time the GLO venture went happily along.
Situated as it is in the triangle of BHX, BRS and CWL one would think that it would have no chance of scheduled commercial routes but someone saw a niche and made a success of it. Both BRS and CWL would love its motorway neighbour too.
matspart - I know that GLO is very busy GA-wise (you said it's the busiest in the UK) but has the Filton closure accounted for even more traffic?