well, their pts costs aren't too bad really! (i can take a decent valkyrie for about 170pts)
the big thin is that for the most part, they are either way over-priced for what they can do or else seriously under-priced considering the devastation they leave behind!
imperial flyers for example, especially the navy fighter planes have a lot of one-shot deal weapons like hunter-killers & hellstrikes. (basically just a fancier named hunter-killer missile!) with only BS3, roughly half your shots miss and when you can only make say 6-8 shots and then you're stuck with say a single lascannon, it's really not worth the big points investment sadly...
now orky flyers on the other hand, get a lot of 'guess' range weapons and twin-linked stuff, so their horrid BS2 really isn't that much of a problem! now consider that a fighter bomber is fairly cheaper than the valkyrie or vulture, and you can see why there's all the complaints about flyers in general!
admitidly though, the vultre and valkyrie don't have to take any single-shot weapons and they work *much* better if you stick with either twin-linked guns and/or multiple rocket pods! (damn those things are tasty!
)
cheers!