Here is a list of some of the problems with Apple's iOS Vista. (7) Apple is calling these bugs "hiccups" by the way, if this was a Microsoft product everyone would be screaming and asking for someone's head just saying. This is the list I have found so far from doing a Google search.
1. Battery drain
2. iMessage failing
3. Apps log you out
4. Lock screen bypass (Security Flaws)
5. Gyroscope not calibrated / Sensors Incorrectly Calibrated (Might be more hardware than software iPhone 5c & 5s)
6. Apple Maps still messed up
7. Apple Music Player does not keep track of last song played after being closed
8. Apple Audiobooks does not use chapter information any longer (Books are now one big audio file)
9. Multitasking issues
10. Many users with visual impairments or motion sensitivity feel sick using iOS Vista (I don't think this is a real issue it can be turned off but people are still complaining about it)
11. UI Changes: toolbar tint, problems with new full-screen navigation, new home screen icon sizes; no <title> usage on iPhone; possible conflicts with new gestures.
12. HTML5 markup: video tracks, <progress>, REMOVED support for input type=datetime
13. HTML5 APIs: Page Visibility, AirPlay API, canvas enhancements, REMOVED support for Shared Workers, Web Speech Synthesis API, unprefixed Web Audio and Animation Timing, Mutation Observer and other minor additions.
14. BIG PROBLEM with WebSQL using more than 5Mb
15. CSS: Regions, Sticky position, FlexBox, ClipPath, unprefixed Transitions and other enhancements
16. Home Screen webapps: SEVERAL SEVERE PROBLEMS (for example, no alert support!)
17. Native webapps: Web View Pagination, JavaScript runtime for native apps and video playing new abilities
18. iOS 7 car integration problems (I would suggest that you do a hard reset of your iPhone, once the phone turns back on you should be able to connect to the stereo, no matter what make it is)
19. Improperly sized wallpapers and no apparent way to fix them
20. Push Notifications tied to the Apple store not working and major security risk.