Having installed ios8 on my iPad i have to say am utterly unimpressed.
A whole year of development and it runs slower than ios7, with literally nothing new of note - no nice design changes, no killer apps, nada. The calendar is still horrible, the mail client is as bad as ever with exchange support, and Safari just gets slower and buggier.
For comparison, I've upgraded various other systems and devices over the last few months - Windows 7 to 8, RedHat 5 to 6, Windows Server 2008 to 2012, Windows Phone 8 to 8.1 and Mavericks to Yosemite. All of these have delivered measurably better performance than before, on the same hardware.
This update is a joke.