Can someone explain why this launch was different? I thought SpaceX was already landing rockets?

Starship. New class of rocket. Massively capacity compared to Falcon. 

It’s like comparing a freight truck and a cargo ship.

TL;DR: precision

This is the first time they caught the booster at the launch site using the "chopsticks" (the big mechanical arms).

All the other landings were on floating platforms in the ocean, or concrete landing pads miles away from the launch site — not on the launch pad itself.

Starship and the booster combined are almost 400 feet tall, the booster is about 230. Something like 700 tons I think? Much bigger than anything else anyone has landed. Also being reusable and the fuel being methane means if it works not only is the moon landing much more realistic but also Starlink (the current version is just a precursor)