"Slide to answer" alternative on Lollipop
If you're using Samsung Galaxy S-series, you can change the call answering and ending options in Settings > Accessibility > More settings > Answering and Ending calls. I didn't like the way it worked, I now have it set up so all I press is the home key.

The other one is Single tap mode, which is like its name, answering/rejecting incoming calls with a single tap.



Image courtesy of AndroidCentral