As the title may suggest, Transformers: Orion Pax is a one-shot that focuses on the character of Orion Pax/Optimus Prime. Whilst its certainly readable, this is an issue that will be highly swayed on your liking for the character (I’m under the impression most people are a fan of Optimus anyway).
First, the official description from IDW:
BEFORE OPTIMUS PRIME—there was Orion Pax! Four million years ago, the future leader of the AUTOBOTS disappeared into the Cybertronian wilderness to save a friend. What happened next would take him to the very brink—and have startling repercussions on the current comics!
As for the plot itself, it is certainly interesting, but it is none the less used as a simple vehicle for Orion at times. As a one-shot highlighting a certain character, it should come as no surprise that he gets most of the attention, with a lot of the dialogue and action coming from the titular character throughout the issue. The result is an issue that highlights the character, yet the writing lacks any depth as a result.
That said, the plot does have a few twists at the end, but these may also suffer as a result of the title being a one-shot. Spread out over a few issues (which other characters have had to themselves in the past) this issue could of explored various aspects in more depth, and the actual plot twists would have had a greater impact.
There are other characters, of course, and these do deliver some form of fan service to any transformers fans. Some of the current cast, such as Rung make an appearance, as do more historical characters that are crucial to the background and lore, such as Zeta Prime.
In terms of artwork and how the issue looks, its not as dark as the current Transformers comics. This is certainly a change, but it does affect the title as well. The opening page, for instance, puts Optimus in a somewhat compromised situation. This is a dangerous scenario that’s almost ruined by the bright, clear blue skies that surround the rest of the page. Yet, this is set in earlier times, so the color change might please some, showing a different time from the current setting.
In short, this issue still highly revolves around your liking for Optimus Prime / Orion Pax. For those that do, they’re certainly going to find a lot to read and look into here anyway.