Though this project is called Trinity, this first issue seems to me to be far more focused on the interaction between Superman and Wonder Woman. Oh, Batman makes an appearance, and a fairly important one, but it's the relationship between Wonder Woman and Superman, who have never met before, that seemed like the strong point of the story so far. At any rate, it's clear that Wagner is approaching these characters early on in their careers, but he still treats them as though they have already built up their icon status. The continuity is a little shaky for those who know their DC Universe at all, but if you put that aside, you get a strong story that gets to the core of these characters with stunning artwork.
Wagner's artwork is a rare treat, made all the more so by the fact that his current work is more polished, reflecting his years of experience, but it still has the energy and stylistic flair that he brought to early work like Grendel and Mage. I'm reminded of everyone from Tim Sale to Rick Burchett to Tony Harris, among others, and Wagner brings an approach to these characters that is familiar and fresh at the same time. His work on Metropolis is something of a standout, but what strikes me are some of his action sequences, which are fluid and exciting. In particular, it does this old school super-hero fan's heart good to see Superman and Wonder Woman fighting alongside one another so effectively. The final chapter that sees these two charging through the lair of the villains is made up of several spectacular visual sequences.
This mini-series promised the first meeting of these three heroes, but it's really only Wonder Woman who is new to this world, as Batman and Superman already know each other. Their villains have also cross-pollinated already, and Wagner uses one of the more obvious Bat-villains (not the Joker, the other one) along with a somewhat idiosyncratic choice for Superman villain and what I think is a new Wonder Woman villain to make up a triumvirate of interesting foes, all guided by someone dangerous enough to threaten these three powerhouse heroes. Given the space of a prestige issue, Wagner spends a fair amount of time establishing two of his heroic leads and all three villains, and he does it well, all the while starting the plot in motion.
Wagner does sort of play fast and loose with the continuity elements here, playing around with both pre-Crisis and post-Crisis elements. The result can be confusing if you try to figure out how this fits into continuity, and the much-hyped "Superman and Batman's first meeting with Wonder Woman" is probably not the best mindset to approach the series with. Instead, think of this as about as in-continuity as your average episode of Smallville and you'll have a much better time.
There's a lot going on here that might not be immediately obvious, and Wagner has crafted a tale worthy of the prestige format. His choice of villains and story structure hearken back to Silver Age cliche (in a good way), but the modern narration and characterization, not to mention the sheer style of the piece, make it anything but a retro curiosity.