Not particularly good, though some effort has been made to make sense of the battle.
In the first place, there are numerous typos. Which are somewhat forgivable given that English is apparently not the author's first language. However, the book is promoted as if it contains scenarios and information for fighting the battle, or perhaps fighting a campaign based upon the Betio portion of the Tarawa Campaign. The problem is that none of this actually appears in any useful capacity.
There is one generic scenario, not specific to Tarawa. There are no Orders of Battle. Army lists use the "Flames of War" format, right down to the rating of units per morale as "Trained/Veteran/Conscript," or "Confident/Reluctant/Elite." The units given aren't specific to Tarawa, either, though the authors do name units that were on Betio or Maki and used similar organizations. Most of the Japanese armored vehicles discussed (the Ka-Mi, the So-Ki, the Type 89) have nothing to do with Tarawa.
The images are mostly rendered, and someone clearly put a lot of effort into them. However, it would be nice to see actual miniatures in action.
In sum, this appears to be an unofficial Flames of War "Army Book," named for Tarawa but actually focused upon generic island landings circa 1943-44. There isn't anything, beyond the timeline, that absolutely "screams" Tarawa, and that information would be much more useful if placed in a context with scenarios, campaigns, etc. The lack of an Order of Battle is particularly frustrating.