If it was cheaper, I'd feel better about having bought it.
Okay, so the "Civil War" was a major event in Marvel Comics that set the narrative for most of their titles for years to come. It was also a thinly-veiled commentary on post-911 Patriot Act-era America, and set a very gritty, post-modern tone for the company that pretty much existed through the "Siege" storyline when they decided to just pretend like most of it didn't happen.
So if you set the Marvel Heroic Roleplaying game at the beginning of the Bendis-era Avengers, then the Civil War is the obvious follow-up (they have already announced that they will be releasing the Initiative as a sourcebook).
But how does it far as a sourcebook? Well for starters, if you're not setting your MHR campaign in the mid-2000's, all you are really getting is a smattering of NPC's that are often already available as fan-made datafiles on the internet and vague idea about how the creators want you, the "Watcher," to compose adventures.
Let's start with my biggest beef of the book. In the theoretically-playable Marvel characters in the back of the book (since the rules are pretty open-ended about scratch-built PC's; they'd obviously much rather have you play theirs) there are no less than thirteen characters that already appeared in the core rulebook. The new versions are almost entirely identical to the original except for their distinctions and milestones. You get Cap, Iron Man, the Fantastic Four, Spider-Man, and a handful of other iconic heroes. Again. There are some noteworthy new ones, mostly from the Avengers roster like Wasp, Yellowjacket, Wonder Man, and the Sub-Mariner. In addition, there is a "Friends and Foes" section which includes a pretty sizable group of what would be NPC heroes (I guess they are "Watcher characters") which can be tapped into pretty easily.
Second beef: there's a paucity of villains, mostly because the story is largely a hero vs. hero tale. You do get my personal favorite, Doctor Doom, as well as the Thunderbolts (including the Green Goblin, who becomes a much bigger deal later in the story). There is also a write-up on AIM and Hydra, and it is interesting to see how the game handles villainous organizations that way. But that's really it. I'd honestly pay money for a straight-up sourcebook of villain datafiles in a heartbeat, internet or not.
Then there is the plot. This is perhaps the most revealing portion of the book. Not revealing like you learn more about the rules or more about how to design characters, but more about how the writers of the rules imagine the game to be played.
For example, in each Act there is a whole host of conditions, items, etc. that could become either assets or complications. For example, under the Statue of Liberty it says that the location features "Cramped Conditions," and "Symbol of Liberty." Now maybe "Symbol of Liberty" is an asset, in that it would inspire your patriotic-themed hero. Or it's a liability in that threatening to destroy it would give the villain leverage. This represents, I think, the biggest shift in the kind work that a GM has to do in preparing for a scenario, namely identifying various elements in a specific manner as they do.
Finally, there is the actual plot itself, which reveals the biggest weakness of this kind of sourcebook. In the initial rulebook there was a mini-saga that followed the "Breakout" storyline that launched the New Avengers. It was, by most estimations, pretty tightly tied to the plot of the six-comic series. "Civil War" has the same problem, only in trying to loosen the railroading tendencies you get a pretty messy layout for the person running the game.
Let me explain it more clearly. If your PC's manage to subdue supervillain menaces with ease and little personal destruction, eloquently convince members of Congress that they pose no threat, and even manage to seduce Maria Hill into being your personal love muffin, the Superhuman Registration Act will still pass, superheroes will still divide into sides, and still culminate with a showdown at the petrochemical factory. The writers clearly want to give people options in terms of the direction of the plot, but still end up regardless of how things go hitting various milestones (pun intended) that track along the Civil War comic books.
This, I think, is a problem with this kind of supplement. First, you're tying the hands of the GM (unless he or she just says, "I'm not doing this story as written" which would be a great idea). Second, a lot of people read the comic books, so they know the petrochemical plant is a trap by pro-registration forces, they know the head of Damage Control was ultimately responsible for the Stamford disaster, etc.
It would be like if the Star Wars RPG published a sourcebook for Episodes IV-VI, and told the GM that in the first act, the Death Star would be destroyed, another built, and then it destroyed in the third act. Who'd want to play in that campaign. I'd play in one where the Death Star could survive the battle of Yavin and then tear up the galaxy, but Civil War even goes so far as to say "hey, Watcher, feel free to kill off a major figure in the final battle, like in the comics." (Paraphrased, but only a little.)
Here is what I want, and I think most people considering running the game would want: first, datafiles to show how to emulate certain powers, etc. using the sketchy MHR rules; second, original plots that can either be used directly or inspire our own stories that could be run with players who have actually (shockingly enough) read Marvel Comics; third, a softcover book. There's no reasons why the main rulebook is a paperback at $30 and the supplement is a hardback at $40. That's backwards and can do nothing but discourage me from buying future supplements.