Besides more abstract reasons, such as being incredibly boring, here are the concrete reasons for why it was the worst:

a) The entire Mac lineup is outdated and badly in need of refresh and/or redesign. Apple failed to deliver its long-overdue updates to an enormous segment of its product line, and in one of the busiest times of the year for the market (college).

b) There was a substantial glitch in one of the demos.

c) The woman that presented the new Music app had a horrible presentation and failed to get the crowd enthused about the product even slightly (see the section where she tried to get everyone to sing along). She tried to come across as having a big personality and failed in that attempt.

d) There have never been weaker product features. The only big updates to the Mac are Siri, a universal clipboard, and a new file system. The only big updates to iOS are messages, Siri, and a new lockscreen. The lockscreen itself is a relic of older days: it has no place in the new iPhone when TouchID can unlock the phone before you finish taking it out of your pocket.

e) Swift Playgrounds, Home, and WatchOS will be important to less than 10% of Apple's total customer base, combined. Swift remains an inappropriate language for a beginner programmer to learn.

f) Many of these updates are not innovations, but are features that have been included on competitors devices for multiple years. Siri on the Mac is answered by Cortana in 2015 and Google Now in 2014. Organizing photos app location was available in iPhoto as early as 2011 (which, by the way, is a terrible feature which no one ever used). Organizing photos with intelligent deep learning is already available with Google Photos, and Google Photos also comes with unlimited cloud storage. Lyrics in the Music app? I had lyrics in the music app on my iPod Touch 2G in 2008! New feature my ass.

g) The Music app continues to place a focus on Apple Music, and wastes tons of screen space for anyone that is not a subscriber to that service.

h) "Intelligent emojification" and bigger emojis are joke features that shouldn't impress anyone above the age of 14. These and many of the other additions to the message app hinder communication instead of enhancing it. I'm a business professional and I want to send a message to my boss: now I have to wade through the minefield that is the app drawer, stickers, tapbacks, message effects, digital touch, handwriting, the stupid walkie-talkie button, and the button to add photos, all with 100% accuracy, 100% of the time, to avoid sending an inappropriate message. Anyone with a job should hate these features.

i) Countless new ways to use 3D Touch, none of which can be used on the vast majority of devices that iOS 10 supports. These features were only added to make use of a hardware feature that is completely useless. Each and every one of these software updates could have been implemented in legacy devices by just having the user tap the screen for a longer duration. Developers also hate supporting these features, as most devs only make money when the user is in the app.

I don't recall an Apple presentation ever being worse than this one, and I have watched them religiously for more years than I can count. CMV.