The high concept behind the series involves Persona, supernatural demons connected to individual people. These individuals can call forth their Persona, usually to battle demons and other supernatural forces. In other words, think Poke'mon, but without the cute creatures and with a bit of an edge.
Persona -trinity soul- revolves around two brothers, Shin and Jun, who return home to live with their estranged eldest brother, Ryou. As if moving in with a brother they hardly know isn't enough, a series of odd events begin to manifest in the town. Eventually, the brothers are drawn into a psychic war where they must bond with their Persona to defend the supernatural conflict from spilling into the real world.
Or something like that. It's really hard to discuss Persona -trinity soul- without going into massive details about Persona 3's plot. Or rather, concepts introduced in the game that make it over to the series. Outsiders can come into the series and enjoy themselves, but at the same time, much of what goes on during the series will escape them. Even smaller events, like why the series spends so much time focusing on the brothers' school life, will confuse some viewers. As the series develops, concepts become even more complicated. It doesn't stop to explain and the few times it does, you still won't fully comprehend everything.
Part of the issue lies with the series being so connected with the game. The other is just poor pacing and planning. Though the series spends a lot of time dealing with the brothers, it doesn't take the time to really develop their characters. All three fit into stereotypical molds and rarely venture outside some prescribed pattern.
The included art book is neat, and goes a little beyond what most art books offer. There's a detailed list of plot summaries and short poems/ quotes that go along with each. Additionally, there's a series of detailed images of characters accompanied by little facts and tidbits about each. Some include in-show facts; others go into the meanings behind names. It's cool stuff. There's also a series of four-panel comics in the back.
Persona -trinity soul- is an okay anime that will appeal to fans of the series more than your average anime fan. Fans will get more out of the plot, while others will either give up out of confusion or pause every few seconds for a Wikipedia check.