I was a bit confused by the set too. My dad had an old Technic crane set, and it was a beautiful, solid, elegant thing. My girlfriend got me the new Mobile Crane for Christmas, and while I greatly enjoyed the build, and it has some very interesting parts (8 identical wheels!) there do seem to be some odd things about the design. The turntable isn't "controlled" at all, the pneumatics, as has been mentioned, are a bit half-done (I'd expected air tanks, even a motorised compressor) and the motor really seems to struggle.
I have 6 fresh AAs of a passable quality but the boom takes literally (and I mean literally in the sense of "actually", not "not at all" as seems to be The Fashion) minutes to extend.
I'm wondering if I built it a bit wrong - I seem to have the choice of either making the string go in and out, or of having the string go in and out at the same time as the boom. Surely it should be one or the other, though the mechanism does what I'd expected.
The base is a rather nice design, but the crane itself leaves me a bit cold. I'm wondering about making a new crane jib based on a Mindstorms set with multiple high-torque motors.