There are lots of game review video channels on Youtube and I have watched many to see if I'd like a game and to get a detailed explanation of how a game is played. This can give more information than you can get from reading the rules provided with the game. Some sites are just reviews but others have a full play through of a complete game.
Of videos that explain how a game is played, my favourite is Rodney Smith of Watch It Played.
For video reviews I go to Dice Tower with Tom Vassel, and Foster the Meeple. I also look at Shut Up & Sit Down, Before You Play, and Becca Scott on the Geek & Sundry site.
To watch a full play through I go to Will Weaton's Table Top or Becca Scott (both on the Geek & Sundry site), Before You Play, and Dad vs. Daughter. Also on the Watch It Played channel, Paula Demming does solo game play throughs. Board Game Geek, the most popular game review website, also has a video channel called Game Night that does a full play through of many games.
