The Big Bang series has for many years given us a solid historical overview of weapons development, distilling its information from many public sources. The US Army Future Combat System supplement is one of my favorites of the line, since it attempts to sort out what the future of the US Army (circa 2003 when it was written) would look like from procurement, demonstrations, prototypes and other materials. It also demonstrates the two areas where I feel the Big Bang line could improve the most, so it's what I selected from the line to write an in-depth review of.
Your typical Big Bang entry is a detailed history of the need for the weapon, the process by which the weapon was developed, a comparison to past and contemporary weapons, and then some stats in various systems so that people can pick out the weapons they want and the system they want to put it in.
To the extent that this approach is justified, Big Bang does a good job with it. My criticisms of this approach are more based on my concern that the Big List Of Guns we see in many modern RPGs is rarely justified in the mechanics either by realism, tactical or strategic game decisionmaking, or narrative. (Is someone really going to tell me which of two extremely similar cartridges are going to deliver 2d4 damage and which are going to deliver 2d6 damage in a way that is going to make me interested in choosing between them?) Whatever beef I have with the Big List Of Guns concept as implemented in RPGs, Big Bang didn't invent it and at the very least it attempts to situate the guns in the needs of a particular fighting force (the US Army) in a particular time frame (what the US Army thought it would be doing in the next 5-10 years.)
This particular supplement focuses on the US Army Future Combat Systems developments. I actually like it better as it is - a snapshot of what we thought in 2003 that Future Combat Systems development would look like. In 2003 we barely launched the Iraq War, and didn't know what the immediate needs of the Army would be in that time frame. The entries reflect this, with descriptions of interim projects ordered to fit into interstitial periods between when older weapons were to broken-down to use and when newer weapons could make it through development. I sort of hope the supplement isn't updated as time goes on and what the Army's working on changes. I want to see this as a historical document.
The content of the supplement is well-covered in other reviews: a list of guns, cartridges and other types of weapons, how they were intended to be developed, and how they function in several systems. I won't go too much farther into it than that. The supplement is extremely well laid out for printing (no background images; all images are already greyscaled, used sparingly, and tables are clean and clear). Bookmarks can get you straight to the weapon you want (though frankly for laymen remembering which weapon belongs to which name can be difficult.)
If there was one area that I would urge the creator of the Big Bang series in general to address, it would be in expanding the supplements beyond the "official" story of the weapons detailed. Often times the story of a weapon extends beyond what it was intended for, how good it was, and how much it cost. Soldiers have always manipulated and customized their weapons and their uses. Corruption and incompetence cause weapon development to go off the rails. Weapons develop reputations and those reputations may be the flashpoint for internal conflicts inside organizations and fighting forces. (Ask the Army about the A-10. Now ask the Air Force!) I would love to see Big Bang entries, especially those that are forward-looking talk about potential problems that the weapons described might run into, or potential advantages that were unplanned-for. In reality, the Future Combat Systems program was cancelled in 2009; a review of the program blamed the premature acceleration of a major internal milestone. That could be an interesting problem for those who are testing or stuck with weapons of various kinds - only getting part of a "system" that was meant to work together.
If the Big Bang series is aimed at games where we're playing soldiers (not, say, members of the House Armed Services Committee - wait, why has nobody written this game?!?!) then let's see some thinking about what might work or not work about a weapon in the field. Heck, in a supplement about weapons systems that aren't out yet, you can just extrapolate it yourself!
That's a lot of words explaining a critique that probably doesn't matter much in the grand scheme of things. All in all, the Big Bang supplements are well worth their inexpensive price, and are much more interesting than your typical "Big List Of Guns" supplements since they attempt to situate the weapons within a historical moment and organizational context, and are well-organized and easy to use. They cross many system lines and if you're looking for cool stuff for soldiering games (or for my upcoming game about being in the House Armed Services Committee; ORIGINAL IDEA DO NOT STEAL), you should definitely check them out.