I had a Nano and a Ruger LC9 to compare, side by side. (I'm a big Beretta fan.)
The first thing I wasn't crazy about with the Nano is it has no slide lock. The magazine is apparently locked open when the last round is fired, but you can't remove a magazine and lock the slide back.
I also didn't like the fact its magazine held six rounds, but the LC9 has a 9-round mag.
The Nano was priced considerably higher.
The Nano is definitely a blockier-looking pistol.