Thanks for your feedback! Actually, I barely spent anything on the trailer--only the cost of the voice actress. I did everything else myself in a couple weeks, using the assets I already had from the game. But I do agree that it is boring without the music I wrote for it. The trouble with trailers for visual novels is that there isn't a lot of action to show, and most of the onscreen movement comes from slow zooms of the backgrounds and characters, with maybe a few clips of the text. Thankfully in my game, there are a lot of cinematic/animated moments, but back when I made this trailer, I had only programmed the first 45 minutes of the game (which is the demo) so I had to fabricate a few of the later scenes I was planning. I do think I should probably make a second, shorter demo for it that uses a lot more of the animated battle scenes.
You are definitely right that different types of advertising is needed for different places online. I plan to experiment with your idea of using gifs and I may try to put together a shorter trailer with more of the animated parts of the game on display.