I was perfectly happy with the 3G service on my iPhone 4, and the HSPA+ service on family members' 4Ses was nice, but I didn't expect to care much about the LTE service on my iPhone 5.
I've gotta tell you, it's very nice, and pulling up pages feels like you're on WiFi. But the first time I really noticed it was when I was sitting in a parking lot and asked my phone to pull down a 1/2 hour podcast. I pressed the little download button and watched in amazement as it downloaded in a couple of seconds. I pulled down the Speedtest.net app (also quick) and was stunned to see that I was getting 20 Mb/s down, nearly double the speed of my home connection.
It's a bit like the retina display. No one actually needs one, but it's just so much nicer than what you had before that you can't help but love it. Given that the power draw on the newer chipsets means battery life isn't gone, it's turned out to be a surprise great feature.