To tell you the truth, it's growing on me. When I first encountered iOS 9's lowercase keyboard, I felt confused and dismayed. Unmoored, if you will, suddenly separated from iOS's venerable ALL CAPS keyboard. Now that I'm a week in, I'm starting to feel better about iOS 9's case-shifting keyboard. The lowercase letters don't look so strange, and it's easier to see if I have the Shift key engaged.
If you miss the ALL CAPS keyboard, there is a toggle switch buried in Settings that will bring it back.
Head to Settings > General > Accessibility > Keyboard and turn off the toggle switch for Show Lowercase Keys.
In related news, iOS 9 has added an option to turn off the character preview that shows you which key your finger is tapping (and covering). I find this feature incredibly useful, particularly when carefully entering passwords. If you feel differently, you can disable it by going to Settings > General > Keyboard and turning off the toggle switch for Character Preview.
For more, see our complete guide to iOS 9.