This is a strange one; one of those films that the critics panned but audiences loved. I finally gave in to the temptation of watching this after being recommended by a number of friends, and my honest opinion is that it falls somewhere in between the two.
Liam Neeson is superb, but the same cannot be said of the rest of the cast; the action sequences are serviceable but certainly not amazing, and the the storyline is bog-standard revenge thriller, nothing we haven't seen before. I felt that some of the emotional beats were too forced, but I guess it plays on every parent's fear of their child being kidnapped, which is probably why it was so successful with audiences.
Overall, though, while vaguely exciting in parts and driven by a powerful Neeson performance, this is simply a decent film; nothing more, nothing less.
If you like this, I would recommend 'Man on Fire' or 'Memento', both of which are very different films but do the whole revenge thing much better.