Best bet is to call KLM HR dept. direct to ask for entry requirements. Alternatively you can call KLM-Cityhopper/KLM Cityhopper-UK, not sure- but I thought they still recruit indepent. Same list/carreer.
Would expect that in principle a JAA license is required and the right to live & work in the EU. Depending on background there are additional demands regarding experience.
KLM is very much fun to work for [although there have been very busy periods in the past]. But I am pretty sure that goes for many other airliners like BA, AF, LH, AC, etc.. Guess regardless where you work the 'fun' is in you.
Ciao,