It depends on what the game trailer shows. For me, a trailer that shows cinematics/a well-animated video of characters doing things that you can't do in-game, does not appeal to me. Yes, it's shiny and pretty, but it's not telling me the sort of fun that I can have if I purchase that product. Game trailers that show in-game footage of characters in the meat of the action are what get me interested. Take the new trailer for the Skyward Sword. That's all in-game graphics and environments. Areas I'll get to see and explore, with NPCs I'll get to interact with. That, more than anything, makes me want to play the game, because it's giving me the game at face value and the face is pretty damn good looking. Showing off only the cutscene cinematics in commercials makes me feel like a game is hiding something that it really should be showing.