Instruments can be hard but I sat it today and there were only about 3 Qs on gyros/compasses and nearly 30 on flight directors and GPWS - nice! Almost as easy as Comms.
Airframes/Systems is a huge subject to learn and I'd say General Nav is quite evil too as you're required to not only know how to do all the stuff but do it quickly and accurately.
POF and Met are supposedly tough but I recognised at least half the Qs straight from feedback and that's a great help!