There is no right answer that we know of. Below I present some evidence both for and against the ending being halo-induced; both arguments have pretty good evidence in support of them. Although there has recently been a new series set 10 years after the movie, we still don't know whether or not it is halo-induced (see Edit 2). After doing this research, my opinion is that the ending was halo-induced, however this is more of a gut feeling than anything else!
This is actually discussed on the Wikipedia article for the film (emphasis mine):
The most commonly criticized element of the film is its ending (Source 1, Source 2). The
film has a more traditional "happy ending" which contradicts the tone
of the rest of the picture. This has led to speculation that
this ending is the product of John's imagination, caused by
hallucinations from his forced coma after he is incarcerated. As one
observer mused, "The conclusion of Minority Report strikes me as a
joke Spielberg played on his detractors—an act of perfectly measured
deviltry." (Source 3)
One critic theorized, "...[r]ather than end this Brazil-ian sci-fi
dystopia with the equivalent of that film's shot of its lobotomized
hero, which puts the lie to the immediately previous scene of his
imagined liberation, Spielberg tries to pass off the exact same ending
but without the rimshot, just to see if the audience is paying
attention." (Source 3) Film scholars Nigel Morris and Jason P. Vest point to
a line in the film as possible evidence of this. After Anderton is
captured, Gideon tells him that, "It's actually kind of a rush. They
say you have visions. That your life flashes before your eyes. That
all your dreams come true." (Source 4) While Vest considers the blissful
dream ending a possibility, he questions why Anderton did not imagine
his son as having returned. (Source 5)
However, as pointed out by Praxis in chat, this article explains the tricycle scene:
Re-watch the scene where Anderton pulls up to Lara's house after she
phones Lamar. Sean's tricycle is very deliberately sitting on the
front lawn as if he'd just finished riding it, threw it over, and went
running down the lane. Six years after he was kidnapped.
Just to make the point a bit more obvious; why would Sean be riding a tricycle still six years after he was kidnapped?
I had previously written above the following:
This scene (the tricycle scene), for me at least, confirms that Anderton is dreaming. So
this scene implies that in Anderton's view, his son has returned and
hasn't aged since he last saw him - Anderton probably is dreaming.
Yet, as pointed out in Lèse majesté's comment below, the tricycle is left more as a shrine - it is rusted with weeds growing around it. This suggests that in fact Anderton's son wasn't recently riding the tricycle, just to add more confusion!
This then casts doubt over the tricycle scene - if it was a shrine it could possibly mean that Anderton is dreaming, his son has returned and the shrine is serving as a shrine for when his son went missing but possibly a reminder of the happy ending. Alternatively, it could be reality and that shrine is a testament to Sean's memory. Sorry to leave this as a maybe yes/maybe no answer but it seems like Spielberg intentionally made this one for the audience to make their own mind up about!
A new sequel series has recently aired, also called Minority Report, described by IMDB as follows:
10 years after the end of Precrime in Washington DC one of the three
PreCogs attempts to lead on a normal life while still suffering from
visions of the future. Will they be able to hold it together or
mentally breakdown and give up?
Now, again there is no definitive answer, but it offers us three options:
- The ending of the movie is not halo-induced, the Pre-Cog program was dismantled and we are following one of the three PreCogs 10 years later
- The ending of the movie is halo-induced and this series is merely a continuation of the halo-induced ending in Anderton's mind. Precrime continued operating in the real world.
- the ending of the movie is halo-induced, but this series is not part of that halo-induced aspect; for some reason Precrime was dismantled in reality.
So, even with this new source, we're no closer to knowing. I am still of the opinion that the ending is halo-induced, but as I say above, this is more of a gut feeling than anything that has solid evidence to support it; both interpretations are equally valid unless further evidence is offered by this new series!