Halo 3 ODST:
The trailers have so much passion put into them, and are just fun to watch. It makes me sad that I wasn't around to witness the days when game developers made games because they loved doing it, rather than money...and when people actually made good games
the Halo 3 OSDT ad, damn, that's hard to beat.
I literally couldn't care less about the Halo franchise, but I played the Halo MCC, and while all the games were meh, with the exception of Halo 1, and Halo 3 OSTD, and the fucking union they made couldn't have been better at selling what the game wanted to convey.
If I'm going to co-create it would be with Destiny 2, which I also think is a bad game. But I like that everything in the ad is actually canon in the lore, from how the guardians are experts at dancing, to the fact that they actually danced in the middle of a war zone to get enemy intelligence.