It was OK.
To my mind there have only ever been two good railroad/railway movies made. Buster Keatons "The General" in 1927 and the Ealing classic British Comedy "The Titfield Thunderbolt" from 1953.
Unstoppable is a runaway train movie and once you've seen one runaway train movie you've seen them all. All the same tired old disaster movie cliches are there in great depth. From the relationships of the characters to climactic ending. Even though the tale is based on a true story even the lightest research reveals just how much Hollywood exaggerated things.
That's not to say I didn't enjoy it. I was quite taken in with Tony Scotts direction and the action sequences were well shot. Apparently many of the crashes were actually filmed and not CGI created which in these days of CGI is quite gratifying.
But ultimately I came out of the film feeling quite disappointed.