In a word: Incomplete. What is there is very good, interesting and detailed. Unfortunately, there is a lot more information that, in my opinion, should have been included but was not.
This setting has a very Transhuman feel. Characters can be Mainline Humans, Scientifically Induced Mutants (SIMS), Natural Mutants (NM), Uplifted Animals or possibly Artificial Intelligences (AI). The writers use the Alien Traits presented in the TMB as a baseline for developing their mutations, which I feel works very well and is quite inspired. However, in the discussion it states that baseline humans have a lifespan of about 200 years; however there is no discussion about how this very long lifespan affects Character Creation or Aging. Without further guidance, it should be possible to create a 100 year-old character that has completed 25 terms of service and has an incredible number of skills. Alternately, characters would be only in their early thirties (per the basic assumptions of the TMB) with no explanation of why they didn’t stay in longer. No discussions are made about how these longer life spans have affected society or the rules for military service. After 25 terms, everyone should be Rank 6+; the rules are silent on this issue. There are no careers presented, nor any descriptions of how to alter existing careers for this setting.
The history is interesting and seems to logically lead to the setting as presented; the current year is 2991. There is a nice map of the entire setting showing all the major polities out to the edge of known space. There doesn’t seem to be any regions on the map that are not controlled by one of the great powers. Even the OTU had regions with a lot of independent worlds. This setting doesn’t seem to have such an area.
There are no aliens in the setting, although alien ruins have been found. This leaves things open to the Referee or to future development by Terra/Sol Games. From the hints given in the book it looks like the writers have something in mind.
The Twilight Sector itself is actually a subsector. Only six of the worlds are mapped and detailed. The rest of the map is blank; not even stars are shown. This was another mixed bag for me. The detail of the worlds was very good, several plot hooks are available in every system and there are nice world maps and system maps. But again, while this is the edge of the explored, none of the unexplored is even shown. A lot of work would have to be done by a Referee to develop the unexplored portion of the sector. It would have been nice if one or two unexplored worlds would have been detailed.
The setting also uses the Warp Drive variation from the TMB and FTL radio that travels at the same speed as the ships. This is different and interesting, but no other explanation is given about ship design and no sample ships are included. There is some discussion about how Warp 8 is possible, but since nothing in the TMB rules allow more than a rating of 6, it leaves a big hole in designing ships for the setting. Also, throughout the text there is mention of city-sized ships called Dreadnaughts. No information is actually provided about them, such as where they go (or don’t go), how many other ships they can carry, how big they actually are in tons… nothing.
One of the worlds in the Twilight Sector is Terra/Sol, an exact duplicate of Earth, down to the shape of the continents. Obviously this is one of the big mysteries of the setting. Terra/Sol represents a nice alternate to Earth: alternate countries (Aztec Empire, Republic of the Plains etc), but again, details are lacking. No geopolitical map of Terra/Sol is provided, so even though countries are discussed, the reader doesn’t really know where they are or how much territory they cover.
The artwork is very good overall. There some color pictures, shaded pictures and line drawings; a nice variety of artwork. There are only a few obvious typos, and none that really confused you. Several of the tables could use a bit of formatting (the mutant ability tables specifically), but again nothing that caused significant confusion for me.
This is a mixed review because it is a mixed product. What is there is very good, but there seems to be a lot missing. Future products will no doubt fill in these details, but I was hoping they would actually be in this book. In my opinion, the mutant generation system alone makes it worth the $12. The Transhuman feel of the setting is also very nice and shows how such a setting assumption can be fit into the Traveller rules by Mongoose.
One final note, the book is obviously published under the Open Gaming License that Mongoose has provided for Traveller, but the book itself does not contain a copy of the OGL, nor does it tell you what parts of the book are OGL and what parts are Intellectual Property. This is a BIG miss and needs to be fixed right away.