Written in 1882, The Fixed Period does show it's age a bit. Not so much in the writing, but in the pace of the novel and some of the attitudes expressed. That said, the dialogue-heavy style does make for a very easy read.

What really makes the novel so readable, though, is the central idea: The attempt to build a dystopia from the point of view of the utopian trying to build it.

In this, Trollope very effectively, captures the core point that one person's utopia is a dystopia for many others.