Overall it's a great system, good-looking book, easy-to-understand rules, and contains an engaging beginning mission to try at the end. The way this game breaks everything down to missions and scenes inside a mission, make it far easier to play over a lunch hour too! You can play any era you want- 22nd, 23rd, or 24th century. The book is laid out with the art style of the 24th century (Next Generation/DS9/Voyager).
Art and Layout
The art is fantastic and inspiring, and each chapter is an easy read. Your first three chapters give you a real understanding of what Starfleet is about, and really sets the stage before it gets into the mechanics and character creation in chapters 4 and 5. It's also a refreshing system as a DM to use a system that doesn't solely focus around combat.
Unlike any other system I've played, Star Trek Adventures has players rolling up their origins (or you can pick and choose). Were you born on a homeworld, star base, colony? You'll get stats for certain attributes and disciplines based on that. It's a fun way for players to interact (perhaps they were born on the same planet based on one roll, moved away in the next, and reunited in Starfleet Academy). It's an absolutely fun process.
The real mechanic in Star Trek is science! You can invent a lot of technobabble. If you want to learn what this alien or phenomena is, there's a great observe/hypothesize/test mechanic, and when an engineering problem comes up, the Extended Task mechanic keeps things driven.
Combat can happen, but there's threat involved if you use violence without diplomacy. Starfleet isn't about going in guns blazing. However, if combat is inevitable, it took 2 encounters for my players and I to understand how it properly works. I ended up having to stream-line the process by writing it down in my words in a separate document.
Same with Starship Combat. Having all players new to the system, I essentially wrote down each starship position and the actions they can do from that system (and how much difficulty it would be to roll that). It took one and a half encounters to really know how to fight in space.
The rules appear very easy to understand at first, but also very easy to overlook things. For example, Momentum is what players generate when they succeed so well at a task, and they can do a great many things with it. However, I missed the part where they can only have up to 6 saved at a time, and each successive 'buy' for Momentum has cost increases. In the first mission of Xerxes IV, my players had up to 37 Momentum to guarantee a lot of successful tasks.
The hardest part for me is Threat- the opposite of Momentum. The GM is encouraged to spend it as often as players spend Momentum. I feel I sabatoge my own original mission designs when I have to create a new threat to the environment, but it thankfully gets easier to anticipate these things the more I GM.
I love this game, and have gotten a fair amount of praise and excitement from my players. Character creation is fun and engaging, the gameplay mechanics and rules are fairly easy to understand.