Some features I just can't live without:

* tmux integration. Whether I'm in a remote server or my own machine, just use -CC and I can now use tmux with the same keybindings I would use without tmux.

* Watch for the completion of a command. Especially useful if you happen to be using a language with a slow compiler like Haskell or Rust. Plays a nice ding when the command is done. (This may require shell integration).

* Even if you forgot to run your command with time, iTerm can still tell you the wall clock time of your command. (Shell integration too).

And then just small things that the builtin Terminal doesn't have:

* focus follows mouse * smart selection (for example it could detect a URL and you can select the whole URL, then command-click to open) * copy on select