It's funny/sad how people are expecting Cook to deliver revolutionary new products. How did Steve Jobs do after his return to Apple in 1997? Well, there was the iPod in 2001, iPhone is 2007 and iPad (although it was said to be "just a big iPhone) in 2010. That's three (or two if you exclude the iPad) revolutionary products in 13 years.
iMac? It was basically a refined continuation of the Macintosh. iBook, Powerbook? Laptops. Incredibly refined laptops, but still just laptops.
Apple has never been about brand-new revolutionary products, although they do release those on occasion. They are about constant refinement and iteration. How people keep on missing that all this time is beyond me.
The iMac was pretty revolutionary at the time. An easy to use 1 piece computer for 1k. Ditto with the iBook. Back when competing laptops were 2-3k. And then he actually turned Apple into a software company - iPhoto, iMovie, iTunes and of course FInal Cut Pro which did for $1000 the same thing a $50k edit system did. The software list alone was enormous- Keynote and Pages too. The great software gave you a reason to buy their hardware. Among all this the iPod, iPod nano, iPhone, iPod touch, AppleTV, iPad, Mac mini, Xserve, and many revolutionary refinements of the iMac. It may not have all been revolutionary, but there was a constant flow of new products, attempts, releases, and refinements. Even the CUBE was amazing, but overpriced. He righted the ship. Set a new course for hardware, new products, new operating system(s), and software. He was still taking risks right before he died with FCP X.
But he probably did leave Cook in a tough spot. I think he wasn't quite as on tip of things, understandably, in the end. Perhaps he was moving too fast trying to set Apple on the track be wanted before he left us. But things were being released so fast I think quality control was failing. FCP X, antenna gate, and Siri are good examples.
Tims in now and we've had extreme hardware delays with the iMac. (Isn't supply chain his specialty?) a major screwup with Maps, lengthy delays on the MacPro (jobs was probably killing it) and ios7 which to me is nothing special, just and ugly facelift and a few evolutionary features that other os's have had for 3 years (like fingerprint sensor).
So it's no surprise Tim is undergoing some scrutiny. Steve took a failing company he wasn't involved with and made it the most valuable company in the world. Tim took over a company he was immensely involved with that was also the most successful company in the world and has had nothing but controversy and hardware delays.