Once I figured out when to use MXML (it's great for setting up layouts) and when to use Actionscript (I try to use AS for most everything else), I was happy wit

Once I figured out when to use MXML (it's great for setting up layouts) and when to use Actionscript (I try to use AS for most everything else), I was happy with it: it gets the job done fast, it's object-oriented enough for my purposes, and it's far easier for me to understand than the Flash timeline. Being able to quickly produce AIR apps is another nice use for Flex. I'd recommend starting with Flex Builder (based on Eclipse) which was much easier to get setup than the commandline tools.