In a long post, even by Epic Win's standards, our Castor and Pollux hashed out the following:

So essentially, our consensus on what makes a good OP seem to be as follows:

1. It needs to have an awesome song, one that can stand on its own merits.

2. It should look cool and be fun to watch.

3. In plot-driven series, it should show as little as possible of as yet unrevealed characters or plot points.

4. If possible, it should highlight the characters and setting, but preferably not at the cost of any of the above points.

I think they lean on plot points too much. For example, I did not mind the A6M3 Zero in the OP of Zero no Tsukaima one iota. Also, a big chunk of their argument seems to apply better to ED rather than OP. I suspect that a part of it is a matter of perception: if you watch mostly on DVD, as Steven does, it's trivial to skip OP. On fansubs you have to fast-forward it, or use the slider and add 1:30 mentally.