While from what I have read about it zsh is a nice shell, it doesn't deal with what I find to be the biggest problem with bash, sh, and just about every shell that isn't fish: the horribly ugly and inconsistent syntax. And I think it's rather sad that on what is supposedly the most advanced shell of our generation, you still have to deal with a thousand ridiculous redirections and quoting styles, different delimiter…
The thing I like about fish is the easy history nav. I type "git" and press Up, and I get to go through my history of anything that started with "git" very quickly. I'll often remember I typed an svn command three weeks ago, but forget the parameters, and I'll have it back within 15 seconds. It's like magic!
In bash, you can get it by adding the following to your .inputrc (at least on mac terminal)
"\e[B": history-search-forward
"\e[A": history-search-backward