The Iron Gods Adventure Path is one of the more experimental adventure paths, in that it deals with aliens and technology in a fantasy world. In this way, one might expect that its Player's Guide would have to introduce a lot of new rules material to cover this. However, the adventure path is also about the player characters encountering technology gradually. They don't start in possession of it, but learn of it through play. As such, the Player's Guide actually has a bit of an easier job than those that do need to include many add-on rules.
All things considered, the Iron Gods Player's Guide does a very good job of setting the scene for the players and preparing them for what is to come. It gives just enough information to help them create characters that will fit the adventure path, without giving away too many spoilers of what will happen during it. The first part of the book contains a quite extensive section on “Character Tips”, including archetype suggestions, appropriate animal companions, favoured enemies, languages, and so on. There is also a sidebar on where GMs and players can go for additional information pertinent to the adventure path (books like the Technology Guide, People of the River, and Numeria, Land of Fallen Stars).
An adventure path's Player's Guide needs to do more than just give players an idea of what the adventure path is about; it also needs to let player's know what it's not about. The Iron Gods Player's Guide does a good job of this. Many players may come to the adventure path with expectations of playing alien races from books like People of the Stars. The Player's Guide makes it clear that that's not really what Iron Gods is about, and the only race from that book that is really appropriate is the android (there is also a sidebar with the basic game rules for android characters). Perhaps most importantly, there is another sidebar about the Technic League, informing players that their characters should not be members of the League or have aspirations of joining it. The Technic League is something that some players otherwise might think would be cool to join and it's important that they know in advance that the Technic League plays an adversarial role in the adventure path. It's a mild spoiler, but a necessary one.
The Player's Guide then provides a selection of campaign traits that players can select for their characters. These traits work similarly to the campaign traits in the Wrath of the Righteous Player's Guide in that they are tied to specific events that will come up in the adventure path. However, this time the resolutions are in the first adventure, significantly reducing the concerns I had about the Wrath of the Righteous campaign traits (see the link above). Resolving the events relatively early means GMs won't have to worry as much about character death, change of players, etc. It's also not as necessary for PCs to have one of these traits; the adventure path will work just fine if characters don't take any. I think these are possibly the best balance Paizo has managed so far with regards to campaign traits. These give PCs a strong link to the adventure path, but aren't absolutely necessary.
Although the PCs don't start off the adventure path in possession of technology, the players are still going to need some basic rules on how technology works in the game for when their characters do acquire some. As such, the Player's Guide provides a “Technology Primer”, which contains the Technologist feat and how the standard skills are used with technology. The rules are reprinted directly from the Technology Guide. Some people may baulk at having text duplicated exactly from another book, but it's important to keep in mind that the Iron Gods Player's Guide is available for free, so there's no rip-off occurring here. Also, this provides an easy way for players to get the information they need from the Technology Guide without requiring them to buy the full book and giving away tons of information they shouldn't start off knowing.
Finally, the Player's Guide concludes with a brief overview of Numeria and then of Torch, the town where the adventure path begins. It includes a map of Torch on the final page. I think it would have been nice to have a bit more information about Torch. However, since the PCs aren't necessarily natives of Torch (indeed, there's a good chance they aren't), I can understand keeping the section fairly short. The shortness here also allows for the in-depth character tips earlier, so overall, it's a good trade.
The player's guides for adventure paths have been a bit hit-and-miss in the past, but with more recent ones, they seem to be figuring out what works and what doesn't. The Iron Gods Player's Guide is certainly an important and valuable resource for getting players started on the Iron Gods Adventure Path.