I just upgraded--wish I had not.
My iPad 2 is slower than my 8 year old laptop. It crashes at times with the screen going blank--and the screen freezing for over 5 minutes. Also, as you have experienced as well, faster battery drainage.
I can't even upgrade my iPhone 5--due to some seemingly memory issues which I never experienced in the past. Maybe this is a blessing in disguise given the terrible iOS8 release. Loving some of the features though but comes at an enormous expense of basic functionality. Due to having different iOS's install on my devices, I'm being told my iCloud won't work?