I mean for me - as a bit of technology geek, I have to say it's pretty much everything.
But the internet, that's always going to be the thing that even today still amazes me.

It's just mind blowing that as a kid, the internet wasn't a thing. We got the internet when I started college, and it was dial-up and via something called Surf Time, which meant that between 6pm and midnight on weekdays and 6pm on Friday through to midnight on Sunday, you could dial a local rate number and use the internet, but not get charged for it on your phone bill. It was slow, would disconnect every 2 hours (making Windows service pack updates absolutely impossible, you had to wait until a PC magazine put the update on a CD). During that time, I have seen the birth of Skype, which was revolutionary on dial-up. Hamachi - zero config VPN on dial-up. Social Networks, YouTube.

And now here we are, just 25 years (roughly) later with the ability to stand in the middle of a field, in the middle of nowhere, and stream a 7 hour Oslo to Norway train journey, in 4K just for the sake of it. It really is mind blowing how far we have come, ignoring whether it is good or bad just for a moment, and appreciating what is now possible that wasn't even 15 years ago.