I have mostly enjoyed Arnold's movies, with some exceptions (such as Commando, Twins and the most terrible one where he - oh horror! - gives birth to a child).
To me at least it seems that Collateral Damage is both related with and an opposite of Commando; related because both movies have a revenge plot. Opposite because whilst the latter was characterised by amazingly bad acting and a predictable ending, the former both displays a convincing performance by Arnold and delivers a most surprising - if not shocking - finish.
The plot: I will not reveal too much here in case the reader is yet to watch this move, but the story begins with Arnold losing his family in a bomb blast set off by a terrorist. We witness Arnold's agony, the search for revenge, the captivity in a South American jungle, the friendship with the terrorist's family - and - the incredibly shocking ending.
I know that another review here says that the terrorist is portrayed in a way too sympathetic light, which makes it impossible to despise him as much as we despised the bad guy in Commando. I disagree. And very much so: One quality of Collateral Damage is that we get the impression that there is a human side to the terrorist; we start to understand/think that even his family opposes his evil plans and what he has become; we start assuming that a relationship is developing between Arnold and the terrorist's wife.
In other words, one gets an impression that the plot is taking a particular direction and that the ending will become logical and predictable. But not so! The movie takes us to the conclusion that you can trust no-one, and that nothing should be taken for what it is. And indeed, that fanaticism can override even natural human relations. In my opinion, that is no bad plot at all.
Let me put it like this: If you are looking for something with lots of killing and a banale plot (such as Commando) or explosive sci-fi (such as Total Recall and Terminator II), then Collateral Damage may be an unsuitable choice. But if you want to watch a solid performance by Arnold, an unusual plot and at the same time great action, then Collateral Damage may be what you are looking for.
I may be accused by some of entering deep waters now, but to some extent I would compare parts of the plot in Collateral Damage with the one present in the fantastic Arlington Road. Watch Collateral Damage and you will understand why.