For me, one of the key phrases in the whole book is “…slain, after all man’s devices had failed…” The whole message of the book is that humanity is utterly, utterly defenceless in the face of the invaders. Therefore for humanity to be pro-active in any way in defeating the invaders, even if it is in using biological agents, runs counter to the spirit of the book.

I accept that it is a very abrupt ending, particularly when audiences like their plots to be adeqauetly signposted and meticulously set up, but I believe that there may be suitable structure.

The invaders target hospitals as a source of food which will put up very little resistance. This sets up the fact that they are ingesting disease, as well as portraying them as merciless killers. For those who like their final act grand set pieces, the military have set up a “last stand” around a hospital, where the protagonists have found themselves. However…the humans LOSE, are over-run and the invaders start to feed on the patients. Maybe a final scene where an invader chases the protagonists on foot through the hospital, but starts to exhibit symptoms of infection, which is the clue-in that the invaders are being struck down by bacteria.

I s’pose that doesn’t explain why the red weed dies off, though.

Part of the problem is opportunity: Tom’s character doesn’t spend much time with anyone else, except his daughter. There’s very rarely even an opportunity for him to talk with anyone in a sustained way. Interaction with other people (whether through dialogue or not) might have helped with that.

It would have been a bit of a departure, but perhaps Tom is fundamentally more suspicious of people after killing Tim. This could come to a head with him attacking someone else who (say) talked to his daughter, killing them too. Then we would have the more traditional redemption structure to follow.

More relevently to your comment, I don’t think he needs to actually suffer real loss to progress, though I wouldn’t have objected if he had discovered his son really had been killed. The fear of loss seemed to be almost as important, or perhaps the reluctance to let go. Having Tom going through the feral stage and back up into humanity again might have worked against that. He loses his car earlier; perhaps he steals one back later, kills some more people as mentioned earlier, and does whatever it takes to protect his daughter at the expense of everyone else. Hell, although it’d probably work to have him realise the Error of his Ways, it could even end with him heavily armed, advancing on the house, knowing that the aliens are dead but not even thinking about the aliens, and us not knowing just what he’s going to do any more…

If you’re going to strangle Tim Robbins for that reason, you should do it waaaay earlier, before he’s done all his hollering and banging around.

The son going over the hill scene is symbolic of Tom letting his son go to live his own life. Except it’s not symbolic. They spell it all out in the dialogue and setup.

Good:
Morgan Freeman rocks.

The train and flotilla of corpses were truly eerie.

Alas, the only such evocation was the photos and posters showing the “Have you seen him?” motif repeated over and over.

For the rest, it was simply the Tom Cruise Show re-re-re-dux. For all that he is on film for such a short period of time the Tim Robbins chracterization is so much more vivid than any others.

Cruise’s characterization is set in the first few minutes in the film with his bickering with his ex-wife and the engine block on the kitchen table. ANd he doesn’t grow beyond that point. And for all his adventures, *he* never realizes a real loss — his kids and family, at the end, are hale and healthy, and Cruise’s character doesn’t even learn from the attempt of sacrifice of his on-screen son, but the character is just as much an empty, unrealized shell as at the beginning of the film.