The full version is really better, the free version is just building things again and again, when the full version is a survival and exploration game, not just a sandbox.
The free version didn't interest me at all
. I understood why other people liked it, but it was not my thing.
When they released survival mode, I just about crapped my pants. It's no fun if you get unlimited blocks and you practically can't die, but as soon as they added monsters and the need to collect all the blocks yourself, I was sold. Now I can't stop playing.
I have to say that Minecraft is probably the only game to have genuinly frightened me in a very long time. There's nothing scarier than being several hundred feet underground, getting lost in endless tunnels and running out of wood for torches.