There are a couple of issues with the App Store for iOS as it stands. Probably the one that most of us are most keenly familiar is that finding the gems amongst the hundreds of thousands of distinctly average, or worse, offerings is really hard. I'd hazard a guess that you've probably not downloaded more than a couple of apps speculatively, but most of the apps you have were recommended on Facebook, Twitter or a blog by people you know or trust on such things. There's another problem I'm noticing though, whereby older apps, and perhaps less popular apps are falling into disrepair.
Disrepair is an odd term to apply to software I guess, but it's apt. Where some apps will continue to perform as well as the day they were published, others will suffer from changes in environment. Environment isn't only the hardware or the operating system. In fact, hardware and OS tend to be highly supportive of backwards compatibility, and so apps that are easily confined within those tend to be resilient. However an app's environment is an individual thing, and obeying the laws of machinery, the more complex the system is, the greater the likelihood of failure.
So it happens that where many external and third party parts of an apps environment can be its undoing. A small change in an API that interfaces with a social network or a weather database can simply prevent an app from working. The app has to be updated and it seems to be more and more common to find that the developer is no longer actively supporting the app. Sometimes the problem is an annoyance, and sometimes it's fatal.