There's an awful lot of difference, mostly with new features.
Of the things 2.0 has that 1.1 doesn't, the real big things are post moderation (so users can't see posts until approved), paid subscriptions handling, warning system, moderation centre for keeping an eye on people.
You'll find most mods work better and rely less on theme edits, plus the option to attempt to install on multiple themes direct from package manager.
There's a long list, though, and ideally try it for yourself.
I personally believe 2.0 is better, but 1.1 is stable and considered mature since it's effectively 3 years old with only receiving security patches since then, while 2.0 is still in active development.