Seagal returns to save the world. This time he's on a train, not on a boat, which doesn't change the dynamic of the film at all. And there's your entire premise of the Under Siege sequel, another bland 80s/90s US action flick that got way more recognition than it actually deserved. It's pure action fare and in that sense somewhat decent, but hard to recommend, unless you have a thing for this kind of action cinema.
Ryback goes on vacation with his little niece, a girl not too impressed with her uncle's status. It doesn't take long before terrorists hijack the train they're on and use it as their moving base to deploy some new tech and take the US hostage. Nobody knows where they are located, apart from Ryback and a few heroic others on the train.
I'm not sure what's worse: being under attack from terrorists or knowing Steven Seagal is the only guy who can save you. The action is rather crummy, the bad guys are very lame and the film is completely without any ambition. At least it is quite loud and things go boom from time to time, which makes it somewhat watchable. Far from enjoyable though.