There is very little reliance on special effects in the movie and it keeps a certain amount of suspense throughout (first you think one thing is going on, then another and then back to the first). Yet it is well written and the end result isn't from left field--the clues are throughout.
The film sports a real "up and coming" cast; Brenton Thwaites (also in Maleficent), Olivia Cooke (Bates Motel) and Beau Knapp (Super 8). All of them take the roles given and run with them. The film has a lot of set up before you get to the sci-fi. In some movies this is a recipe for disaster but here it works and most of the reason it works is the three young actors.
The group is traveling cross country and, incidentally, being taunted by a computer hacker. Do they go to chase down the hacker? Or leave it be? Pretty easy to guess that in any film.
You know who they are and sort of care about them. If the movie has tons of action and lots of explosions? Knowing about and caring about doesn't matter nearly as much (just ask Tom Cruise). When the movie is slower paced and more of a mystery? Caring and knowing, on some level, matter.
Is the movie perfect? No. It has some warts but it has its own universe, its own consistent logic and it is evenly paced. Some may not like the set up taking so long? But without that the rest of the film would suffer. Be ready for a deliberately paced film? And you will enjoy The Signal.