After the disappointing Sound of Thunder, I was prepared for Timeline -- another time travel movie -- to be pretty bad too. Not so much, though.
There've really only been two time travel movies that I've liked: The Terminator and Back to the Future. Outside of those, figuring out alternate timelines and resolving paradoxes and keeping track of all the rules that scifi writers create to do those things just makes my brain hurt. Fortunately, Timeline -- like Sound of Thunder -- is more of an adventure story than real scifi. It surpasses Sound of Thunder though by trading in bad CGI for believable characters. A group of time traveling archeologists go back to the Middle Ages, get stuck there, and have to figure out a way home without getting killed by either the French or English armies that are battling in the past over a castle.
The time travel technology is unimaginative and hokey, and there's a lame subplot about an "evil" scientist who's really much more lazy than wicked, but the medieval scenes are convincing and everyone does a nice job of helping us to care about the travelers who get stuck there. It's kind of like watching a time-travel episode of your favorite scifi TV show, only you're not sure who's going to make it out of the past alive and who's not.
Not that it's completely unpredictable though. When the archeologists are studying the castle/battleground in the present and uncover a husband-and-wife tomb, they wonder about the story behind the couple. Not only are you sure that the couple's story will be told once the archeologists go back in time, you're fairly certain that one of them will be intimately involved in it. After all, you've seen at least one time travel movie in your life already, right?
So, the movie has no big surprises and doesn't add anything meaningful to time-travel theories. It's just a fast-paced, entertaining adventure story, and viewed as such, it succeeds. I bought into the various relationships and really wanted to see the characters make it back to their own time.