I wanted to give i3 an honest try, I did and I love it.
The big difference between i3 and xmonad is absence of layout algorithms in i3. You manually arrange the windows. You can call these two different schools of thought in tiling window managers – automatic and manual arrangement of windows. The biggest advantage of manual arrangement is that you can divide the screen in columns and rows, and shift between them using direction keys instead of next or previous window. So no traversing through windows, just shifting to window. I am liking it.
There is more. Every column can have differnet mode of viewing windows – stacked, tabbed or the normal mode. i3 carries window title-bars to identify the windows when in stacked or tabbed mode. Every column can have a separate mode, which is like having multiple layout algorithms in the same screen. I usually go with one column for editor, the other column with log, debug windows, man pages using one of these modes. Or the browser in one and the editor in another. Whenever required, you can go for the full-screen mode for any window you want.
Then there is the brilliant i3-msg utility, using which you can execute commands from command-line. I am going to use them in shell scripts and try.
Otherwise i3 seems familiar to xmonad. It is equally configurable, has vim-style binding, has brilliant documentation and is really efficient in its operations. Although xmonad is more extensible in the sense of coming out with layouts, i3′s manual arrangement gives you a lot more freedom, and not having to choose a layout algorithm. I have used it dedicatedly for more than 2 months now, and I am thinking of keeping it for the long run.