Say what you want about Google/Alphabet as a whole, but Google Flights is incredible. It's absolutely amazing how quickly and largely that Google crushed all its competitors in terms of usability. Kayak, Hipmunk, Orbitz, Skyscanner were all my go-to's at one point but G.Flights is far superior in so many ways. It actually remembers your airline preference between searches. You don't have to beg or change settings to see a few days before or after... every search has a date grid and long-term graph, both which respond almost immediately to additional changes to date ranges. Searching multiple airports or destinations is super easy. Plus the calendar view, with lowest price for every day -- sure other sites have it but only for unfiltered searches. Google's calendar view is updated with every filter change.
There was a time in the 90s when eAAsySabre was publicly available to anyone, and text based searches were simple and fast and so easy. But Google Flights is even better, IMO.
Pretty amazing that sites entirely dependent on travel search seem satisfied with 10-year old UI while Google showed how much better it could be.