I stand by "Signs." I can say I liked it because I realized it wasn't a science fiction movie, but an apocalyptic fantasy, where demons captured the sinners and doubters and took them away.
The aliens were demons. If you remember, toward the end they announce on the TV that, "A low-tech way to defeat the creatures was discovered in the Holy Land." And then in a priest's house the water burns the aliens. Demons have always had an aversion to water, and it makes sense that holy water would burn them.
Seriously, since when has an alien invasion movie been science fiction? We know it's B.S. You either nuke a planet from orbit, or if you really need resources you get them from asteroids or uninhabited planets. If you're watching a movie about alien invaders you're already suspending your disbelief some, so why not suspend it some more.
"Signs" took the classic idea of invaders from beyond, gave it an even more primordial spin, and worked it into a religious allegory of redemption and regaining faith. It also scared me, but then again I went in wanting to be scared and entertained.
Overanalyzing any movie can lead to its downfall. In general as long as the acting is good and there's drama, I'll accept what ever manner of contrived scenarios are showcased. I'll let myself be entertained. Only afterward will I decide whether the movie was any good. (Note that this is what I normally do. When I see true crap like Elektra or Ultraviolet, where the acting is bad and the presentation is lame, I'll decide pretty quick whether I hate the movie.)
But yeah, I liked Signs.