BioWare's Mass Effect 3 launch trailer was great. The high intensity of the final chapter in the sci-fi universe really came through in the slices of action and dramatic moments that were featured.
But this alternative, fan-made trailer using Mass Effect 1 and 3 elements is even better. I love the heavy emphasis on the Reapers, not just through visuals but through speech. Even the music complements it better than the one in the the official trailer.
As someone who has still yet to play Mass Effect 3 (I'm reworking through 2), another launch trailer is welcome. For those of you who have already played the game, perhaps it's a good post-mortem look, without having to look at the ending.