The browser version/demo is still free - and has all of the content you remember from the free version. The full version just has a lot MORE content after the end of the "demo."
you can do all achievements and quests, mine every block to find these caves that have cool things inside, try to find magic or science path end if you didn't finish one of those, try to do things differently, challenge yourself to not have a useful item while playing through the game again, or whatever you can think of. I hope this helps.