First, a remarkable bit of prescience: global worming, to the point that broad daylight in most cities becomes lethal. Considering the publication date, that was a bit spooky.
A few other elements add good SF feel: The UN running compulsory emigration plans to populate the other planets, not of which seem worth living on. That sets up the next major theme: the exiles - uhh, colonists don't have much to do but sit in their group 'hovels', making their living in ways that aren't at all clear, and getting drugged out of their minds. I mean, literally out, and into another (a theme that could have been developed more). Colonization by conscription isn't the critical point, I think; instead, it's the drugs, who sells them, what agencies turn blind eyes, and a semi-legit industry built around the toys that make drugging interesting. The real dramatic tension comes when a competitor shows up to contest the pharmaceutical monopoly. That's also, for me, when things turn murky. After some heavy doses of the new product, the question moves from "what is reality?" to "who is reality?" Dick executes this maneuver with the kind of grace that means you don't even notice when the tight turns have thrown you off the rails until it's way too late.
I don't dispute Dick's place as an innovative and prescient writer. Stil even the biggest fans might not like his entire body of work. If this had been the only of his works that I'd read, I might not be coming back. As it is, this one's going back to the used market in a hurry, and I'll be more selective when approaching his work in the future.