The killer feature for me was setting an "alarm" on a currently running process and getting a notification when it finished. It's not something I've seen in any other terminal. (Using Ubuntu now and missing it.)

Quake-style console. I'm too addicted to it unfortunately.

1. When you exit a terminal it dumps irrelevant stuff rather than just closing the tab.

    ~ % exit 
    
    [Process completed]

2. Cmd + Arrow doesn't doesn't move to the next or last tab. (Cmd + number does work however, but it doesn't show numbers on the tab list like iTerm)

3. Comes with terrible defaults like the screen color.

Probably not a big feature for most, but I work with URLs in the terminal a lot and ⌘+click to immediately open them in the browser is convenient.

I prefer to open a new Terminal only when I need it instead of keeping one open all day (even if that sometimes happens) and I’ve never noticed an increase in CPU usage that’d made me want to check.

> What's the killer feature of iTerm these days?

Panes.

I really like the tmux integration.