I updated from 7.1 to 8.1 . Battery life seems okay, can last more than 12 hours when I didn't on mobile data for the rest of the day. The longest I get was 17 hours. Didn't use my iPhone for games so that'll explain.

No obvious lag that irritates me.
Like the new iMessage and SMS forward.
twice Facebook crashed when I was watching a video.
WiFi okay.
Mobile data okay
Airdrop cannot detect my Macbook, but Macbook can detect my iPhone (frustrated on this)
Been dying to use SwiftKey on iPhone so really love this new keyboard update.

But overall everything is fine currently. Have not yet regretted updating to iOS 8 since Yosemite continuity is really a bunch of help with the iOS 8.

IPhone 5