I couldn't agree with you more. His acting in this movie was really awful. It gave the movie a completely confusing tone...I think it started to go wrong when they got to the part with Mark Wahlberg.
Don't get me wrong, I like him, just in other movies. In this he was just no good.
I liked the movie Signs. Anything with aliens is always worth seeing. I do believe the whole "water as a weakness" was kinda lame. I mean, wouldn't the aliens have known that about themselves before traveling to a place that's made almost entirely out of water?