I presume that you saw the thread below in which I posted a link to the
HackMaster QuickStart Guide. It's goals are somewhat different from the Pathfinder Beginner's Box, but I'd welcome you to compare the two factoring in that one is free.
You could probably squeeze 3 to 4 sessions out of the QSG, if you wanted to get a taste for HackMaster's flavor and mechanics.
Regarding, specifically, the topic of discussion...
In some ways there are more similarities between HackMaster and Pathfinder than you'd expect, ignoring that Pathfinder uses a more abstract combat system. Players in both games would generally be attacking at the same speed IN-game, for instance, although HackMaster puts a heavy focus on second-by-second combat in which movement is constant (although it is at the same basic speed as movement in Pathfinder's abstract system) and players might take damage even if they successfully deflect an attack with their shields.
To focus on that last concept for a second, this is a huge advantage for HackMaster in my mind. In Pathfinder a character is given an armor class which is improved upon by a combination of Dexterity and quality armor. The better the armor you are wearing, the harder you are to hit. In HackMaster, the better the armor you are wearing, the less damage you'll take if you GET hit, but it's actually easier to be hit.
Why? Because if you were wearing 40 pounds of gear (not even counting your backpack filled with your life's lootings) then it is actually going to be harder for you to dodge an attack. This makes HackMaster more realistic and a bit more dangerous. According to the abstract rules of Pathfinder, it's assumed that any miss was a hit which the armor absorbed. I could go on about why this is an Advantage HackMaster example, but the basic of it is that abstracted mechanics negate the random, wild chance of unexpected, awesome things happening. Such as a blocked hit cutting through the defenses and dealing a game-changing amount of damage.
Please don't think I'm knocking Pathfinder, though, as I own a number of the books and am a subscriber.
Beyond the abstract, the most significant difference is the magic and experience level of the games. While I do appreciate Pathfinder offering different "levels" of XP accumulation, HackMaster harkens back to the old school concept of how the accumulation of wealth and experience should be a real accomplishment. It might take you a month of play to hit level 2, for instance - doing so really feels like an achievement. Similarly, HackMaster has dramatically scaled back the use of magic from the 3.0/3.5/4.0/PF concept. Mages are still awesome (and they use spell points, rather than "cast and forget", allowing them to cast the same spell more than once in a day) but many low level PF spells are high level in HackMaster.
Ultimately, then, it's a matter of taste. I believe that a single gamer can be interested in - and enjoy - both, but for me HackMaster scratches all my itches. If you want a high magic campaign with abstract combat and tons of product support, Pathfinder is a good choice. If you want a grittier campaign with a TON of the elements that have been lost from the early editions of D&D, plus a dynamic combat and skill system, then you will want to play HackMaster.
One other issue that's unrelated to mechanics or flavor - if you're a fan of Pathfinder and attempt to collect the books, then you are going to find yourself spending as much as $60 a month just to keep up. The guys who make HackMaster are extremely deliberate - they maintain total control of their product in order to ensure that the quality is off the charts. Consequently, the release schedule is much slower and much easier on the wallet. Last year we saw the release of a beautiful hard cover book (the Hacklopedia of Beasts, which is pretty widely recognized as being the most incredible monster manual ever) 2 print adventures, a pdf adventure and the beta Player's Handbook.
The total cost of these products, if you didn't wait for a sale, was $165, and with them alone you'd have enough gaming material to play in a weekly campaign indefinitely. I'd have to go back and look but I'm pretty sure that Pathfinder put out at least $500 worth of product last year, and maybe more. I just mention it in case cost is an issue.
