Nope, not a ritual. You can look it up in the Basic rules.There's no stores near me that broke the release date so I don't have the PHB for the latest rules, but isn't Knock a ritual spell (10 minutes spellcasting for no expended spell slot)? Also, how often does that drawback to knock actually come into play? Last night in a 3E campaign I'm in we broke into a prison, released some prisoners, and then escaped... And only once out of five lock pick attempts would we have had something negative happen to us. How do you balance unlimited, loud, lengthy lock picking with stealthy, unreliable lock picking?
As for the drawback, it depends on the campaign, I suppose, but most of the time when I've been in a party that needed to pick a lock, stealth was important.