For example, after setting up once, I can press "Ctrl+L" then type "gi" then "Tab" and start typing my search keyword. I don't even have to first go to Google or DDG.
There's a bang for almost every site I frequent, and when a site changes its domain or search URI the bang is updated to reflect it almost immediately with no work on my end.
After a few weeks of acquainting myself with the bang system, I started to see web search from a completely different perspective. I think of a search engine now as less of an "everything index" and more of an "index of contextual searches". My mind, instead of just thinking "I'll google it", thinks "I'll choose a context for it".
Google is like a system-wide grep whose output is altered by advertising, and DDG w/ bangs is like a vast collection of commands piped into a grep.
I keep leaving DDG for the not-always-super-relevant results, and I keep coming back for the privacy, clean interface, and !bang syntax.
I love that using it means my searches are private by default. But the real killer feature is !bang. I find that it's faster to do a Google image search using DDG with "!gi" than to search in Google and then move my hand to the mouse and click "Images".