Someone was bright enough over the weekend to not only download the accidentally-leaked Mass Effect 3 beta, but film themselves playing it.
What we've got here, then, is over 13 minutes of gameplay footage from the singleplayer portion of the game. The first half deals with the Reaper invasion of Earth, the second a mission later in the game.
This is exactly what I saw at Gamescom back in August. The opening bit with the Reeapers is really early in the game, so it's not that spoilerish, but the second section comes later thin the game, so be warned.
[thanks Chris M!]