Yea I seen that one too, didnt really have good reviews as the others. I might just stick with Rockplayer intill I find something better.
Don't let those reviews fool you.
I just looked at a couple of them, and the bad ones are mainly from people who are trying to play either badly formatted videos or non-supported ones.
As with any portable video player, you can not just throw whatever file you find on it, and expect it to play properly, but most of those reviews are from people who are doing just that, and rather than posting a review about Android or the phone in general, they just post bad reviews for video players that try to work with the limitations.
The "cryptic error" one is obviously posted by someone who is trying to play a "Digital Copy" file, which isn't supported on the DX. 720p does actually work on the DX, as long as it is properly formatted.
Droid X plays HD 720p MP4 file, samples in this post, need testing on HDMI plz
Rockplayer can play a lot of different files, but it uses a software-engine for playback. It will play AVI files found all over the web, which is why it is popular, but because it is mostly processor-dependent, it has its limitations.
Act1 uses the build-in hardware support for playback, and of course, for that to work, the files have to play properly in Gallery.