That certainly is a valid HTML5 document, though personally I would still include the <html> tag. Note, the original question was regarding the DOCTYPE, and the <html> tag is not a part of the DOCTYPE. Also, the meta tag can be shortened in HTML5 as well. Here's the ideal starting point, in my opinion.
<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <title>My document</title> <!-- Put styles in the head, but make sure charset is 1st --> </head> <body> <!-- Put scripts just before closing body tag --> </body> </html>