Reasons why I despise Game/Mod Trailers
1. Most if not all videos use that crappy "Lux Aeterna" from Requiem for a Dream, (see #4 for the exception) which has to be the most annoying "song" ever written because it's the most repetitive,
annoying and overused 'song', to the point now, that I immediately shut off ANY video that uses it.
2. As Ceano said, 90% of the trailer is in game cut scenes and pre-rendered cgi and not of the gameplay itself.
3. WORK ON, AND FINISH THE MOD, INSTEAD OF WASTING TIME MAKING A TRAILER!
4. Any trailer that uses music, period. I want to hear the in-game sounds, I don't want to hear dimmu Borgir, or any other speed metal group with Cookie Monster vocals annoying me,
while I'm trying to watch the video. I'd rather hear a voice over of the mod author explaining what the mod is intended to do, how much of it is done etc....
Well I don't think a theatrical trailer I would make would have any of these 4 issues. Let me reply.
1. I would not use Requiem for a Dream music. That has been overused for like 5 years now, and there is MUCH better theatrical music out there.
2. If the trailer is for a mod, it would be 100% ingame footage. None of it would be prerendered. Well, except the 'debut' trailer. But thats because my friend is really into modelling, so it would be a 100% pre-render trailer. But once the mod is almost done, I would make a theatrical one with only ingame footage.
3. Making a trailer does not take away from my time making the mod. Let me put it this way. (with random number for the sake of example) Lets say I spend 10hrs a day working on the mod. Then 4 hours doing random stuff (playing games, hanging with friends, going places, etc) and the other 10 hrs sleeping. If I were to make a trailer, it would simply change to; 10hrs on mod, 2 hrs on random stuff, 2 hrs on trailer, 10 hrs sleeping. You see? The trailer would be deducted from my other time, not the mod making time. Thus having no impact on my work flow.
4. You assume I am stupid and would do something stupid like put metal to a trailer. That is NOT what you do! I would use some of the fantastic music from a orchestral group, like Two Steps From Hell for example. I would never use actual band music for a trailer. Unless its to convey a point like where they use Johnny Cash music for the Splinter Cell Conviction trailer to convey his pain and anger.
See? The things you hate only apply to actual full game trailers, or trailer made by stupid people.

I say you give them a try.