Secrets of the Alchemist by Sigfried Trent offers an in depth look at the Alchemist class as it's available in the Advanced Player's guide. Trent introduces 30 new feats designed with Alchemists PCs in mind, as well as a discussion on what the Alchemist can do as a class, and several suggested builds.
I've often toyed with the idea of playing an Alchemist and I'm glad that Pathfinder has introduced this as a class for PCs, rather than shady NPCs who sit in shops and charge players lots of money for stuff. If you're looking to play this class now, or as a GM want to introduce Alchemists into your game, Secrets of the Alchemist is certainly worth taking a look at. Most of the 30 feats are well balanced and will fit nicely into your game (more on this in a bit).
This PDF starts of with an examination of the Alchemist class and what bearing they'll have on your party. It's worth the read as Trent has put a lot of thought into this and gives an easy to follow overview of the Alchemist which goes a bit above and beyond what's covered in the Advanced Players guide. I finished this section knowing how I'd implement a character in a game, rather than having a few interesting but vague ideas about the Alchemist.
Next we come to the 30 new feats designed for Alchemists. Many of these are great feats which will be eminently useful to your party without breaking the game. Here though, lies my only beef with this supplement. A few of these feats seem to be a bit overpowered and may have some serious effects on game balance.
Take for instance Accurate Assessment. This feat allows a player to take a standard action in a combat round and "learn on statistical value of a foe during combat'. That could be the foe's Strength. Or hit points. Or Will save. To me, this is a bit game breaking on two levels. It first takes the in-game character into the realm of player knowledge. Secondly, it allows players to know things they shouldn't know.
Another such feat is Lighten Weapon, which allows you to use a weapon one size category larger as if it was your own size, with a -2 penalty to hit.
Trent has specific notes on these two feats as well, in which he gives his reasoning for including them. I can agree with his reasoning but I still think they could be potentially game breaking feats.
The good news is there are tons of excellent feats which will add a lot to your game as an Alchemist. Craft Anywhere is one of my favorites, basically allowing you to double the amount of crafting you can do while adventuring. This calls to mind the distracted tinkerer, always with a hand in something.
After detailing the new feats, there are three character build paths for the Alchemist which I think demonstrate a lot of insight into this character and give players and GMs some very viable paths to follow. The first is the Carpet Bomber, who essentially maximizes the number of bombs that can be thrown and their damage. Next is the Mighty Mutant build, which specializes in Mutagens to create a pretty hefty front line Alchemist tank. The last is the Mad Scientist build, who plays more of a support role but can equip a party with some pretty neat stuff.
I'd certainly recommend picking this up, if you keep an eye on a few of the feats and make sure they're not too powerful for your game.
[4 of 5 Stars!]