Forstall was doing a power grab. Saw himself the rightful heir to Mahdi, picked up fights with Sir-ji.
Also was responsible for numerous Pakistaniyats.
No matter how much you drink the FruitCo kool-aid, their UI on the phunwa is much dated. You have screens upon screens of rectangular icons (there is no differentiation between an app drawer and frequently used programs like Android), the only notification you have is from the pulldown --itself copied from Android, no widgets for at a glance information and the pulldown too makes it difficult to dismiss the notification. The app badges look like warts. Despite increasing OS version numbers, the UI has not progressed at all. Fanbois can turn around and claim that it is because it forces people not to learn new UIs, but the reality is, they have been unimaginative.
The biggest blunder though is having skeuomorphic designs. For voice recorder you have a microphone. For notes, you have a ruled notebook, for Passbook you have a fricking shredder! When computers were new, the metaphor to real world objects like a desktop, files and folders were needed to make people comfortable. Now you dont have to make a UI like how it is in the real world. You have a bitmapped display and how does Podcast maker show up? Like a tape recorder! how many teenagers have seen a tape recorder? Why is it in there?
Forstall was heavily in favor of skeuomorphic designs. Others were opposed to it. Also was responsible for Siri and Maps fiasco. Despite what Fruitco tells you, Siri and Maps are fiascos.
So here you have a fella doing power grab, challenging bawarchi, presiding over 2 biggest apple software flops (both touted as hero features) and reigning over an aging dated UI and picking up fights with Sir-ji and Cue (Sir-ji's industrial designs and Eddie Cue's apps/music lock-ins is what selling the iPhunwa, not Forstall's Russell Stover supermarket Chocolate box UI).
Competitors are making progress in the cost front (iPod touch is 300$, Nexus 4 phone is 300$) on the UI front, the fit and finish front and content partnership front. Something has to go.