Most EVN do not have opening movies. It's even questionable whether or not they SHOULD have movies, given their potential quality (or lack thereof). However, I'll admit that a lot of OP movies seem to have a decent amount of effort put into them. I'll give a list of some I knew of / could easily find just to show a variety of what is out there:
The Royal Trap
Upon watching them all in a row I was surprised to find that none of them are really too different from each other, minus three: Katawa Shoujo, Dysfunctional Systems, and Shira Oka which are my favorites of the bunch. The rest of the OP videos are of surprisingly decent quality (I'm not going to comment on the VNs themselves) but are clearly amateur-level. Not that it's a bad thing; we've had that discussion before.
In any case, what did I like so much about those three? Well, let's examine the OTHER movies, and see what they did. Either one or a combination of the following caused the OP to take a turn for the worse:
-too much time spent on characters and their names
-random quotes flying around the screen
-mostly upbeat or intense music
-lyrics and singing, either Japanese or English
-lots of CGs shaking/flying/shattering/inserteffecthere
-too many zooms, fast pans, silly movements on screen
And my "top three" have none of those. In fact, they both have something the others don't -- actual animation. I also believe their success lies in the use of slow songs and no singing (Shira Oka is kind of the odd one out of the three). The more singing you put out there, the easier it is for the singer to slip up. One part of the song that's not sung like a pro and your OP movie goes down a level -- whether it's sung in Japanese or English.
Lastly, 3D effects were implemented in these OP movies, and it worked. There are plenty of JVN which use 3D as well, and I bet that's a key to making their OP look good. It shows a certain level of technical skill. And it's really not that hard to learn either, provided you have something like After Effects to work with. It just takes some dedication.
So I'm going to have to make a decision. I really want to make an OP for Detective Butler, but if I can't pull it off right, I won't include it in the game. You can see examples of what I've done here and here, if you're curious. Note that those are just parodies, but I haven't been slacking off by making them. Remember, each project you make gives you new experience you can draw from and improve upon later. Keep learning, and keep creating!