This was bad in an only moderately amusing way.
It's not like
Cowboys vs Aliens was a huge success, so I don't know who thought this would be a great idea.
The creature effects are kind of awful, as the trailer demonstrates pretty well.
It's not an Asylum film, but it seems to follow the same guidelines, including have a couple of token recognizable actors (Eric Roberts and Vernon Wells, in this case).
I guess it's worth two slimes.