Precisely this is the reason why I didn’t rush with upgrading my daughter’s iPad Air to iOS 8 although the prospects of using a swipe keyboard were almost irresistible. Some people are facing problems like a slower Wi-Fi connection and shorter battery life after upgrading to iOS 8. Other problems that are being faced by those who upgraded to the newer version include audio issues, sluggish overall performance, problems with messaging and of course, as mentioned above, a fast battery draining.
Most of the people who are reporting such problems according to this Apple Support Community thread, are using iPad Air, iPad many with the retina display an iPhone 5S. According to this Mac Rumors blog post, even people who have purchased the iPhone 6 are facing problems with iOS 8. Here is an 11-page thread listing all the problems people are facing after the upgrade.
My advice would be, if you haven’t upgraded, just wait for a while for things to settle.