The Combatant

Per week on Paizo's forums there are at least two threads discussing the Fighter class and what may or may not be wrong with it. In these threads there are common themes to proposed fixes. The Combatant in this product feels like it reflects a number of those proposed fixes despite it's insistence that it is not attempting to replace the fighter.
Essentially the Combatant is the fighter at it's core but with the following differences.
Good Reflex save.
4+INT skill ranks per level.
Acrobatics is a class skill.
Does not need dex requirement for TWF.
The biggest change, Armor/Weapon training is absent, and in it's place are Martial Art Styles. Martial art styles are combat styles associated with a number of feats. If you possess feats within a martial art style you have then you get bonus abilities based on the number of feats you have of that style.
For example if you have 3-5 feats of the archery style, you may ignore up to half your level in circumstance penalties to ranged attacks and stealth becomes a class skill. As you gain more archery feats you get up to 5 more abilities of increasing strength. Some of the feats are on multiple style lists so since you gain 3 martial art styles throughout your levels, you can get a number of extra abilities if you synch them up. The abilities themselves are either obvious numerical bonuses or something amazingly complementary. (like pounce) Overall these are huge boosts of power and versatility making the Combatant a pretty competent beast in combat.
The product also comes with a number of new combat feats and honestly, if you don't use the Combatant class you'll want to use the feats. A lot of them are amazing. A few feel very at home with a monk and a number I would call Must Haves.
Overall for the price of one dollar you're getting a lot. A spectacular class AND useable feats. Very useable feats. The price takes this from being a nice product to one that is silly not to buy.

Retrospective

After having this class for a while I have to say that it is not all that popular of a pick. If you're looking for a fighter fix for a buck then this is your guy but the feats inside have counterparts elsewhere and if you collect good combat feats and Fighter support then this class falls a bit short. Between Bravery Feats, Fighter Nuances, the new Fighter options from Paizo's Weapon Master Handbook, and stamina, the fighter is a beast. And even cheaper than that you can pick up Dreamscarred Press' Path of War if you want to replace the Fighter rather than fix it up. I guess what I'm saying is that the appeal of this product greatly depends on your previous collection and your budget. It is pretty much a better fighter. but doesn't have much support beyond the base class so if you're popping it in for a mostly Core Rulebook game this will shine a lot but the power creep for martial classes kind of stepped up when it comes to peripheral material.  

You can find this over on Paizo.com here.