Then they lost focus. The app has not improved an ounce since then (seriously why is 'open now' not a default filter) and they've spent a lot of time doing shady things or complaining about other companies. They've tried to get into reservations, delivery, and non-food services but with half-assed attempts at each. They also did a really bad job at maintaining a healthy reviewer community (Google has done much better).
It's a shame because I don't think any other app took the lead here. Yelp just walked backwards into the pack.