I love the flexibility and breadth of things you can do with objective-c/c++. It's downsides mostly come from syntax, container class getting/setting is way too verbose, same with string operations. If there was a special syntax for just string and container classes, large swaths of my code would be smaller.
UIKit view controller classes are also not flexible enough, and crap out in a lot of custom multithreaded operations when they shouldn't. I could reproduce the same behavior with my own classes (animations, transitions, view control, etc) using just basic UIView classes and it would work significantly better.