So my group is trying out Pathfinder for our next campaign, with me as DM. I decided to run the Adventure 'Hollow's Last Hope' and the PCs (a gunslinger, an alchemist, a swashbuckler, and a barbarian) got to the first encounter
SPOILERS AHEAD (Just in case)
It was the fight between the hobgoblin hunter and his two crows, and he was using a firefoot fennec as bait. The crows were 1/4 CR, the hobgoblin 1/2.
The party absolutely DECIMATED them. They barely got a hit off, and were easily taken care of.
Is this just because 1. I'm still a bit unfamiliar with the Pathfinder rules, so I could use them to their best advantage, 2. It's a small encounter that doesn't add much to the overall story, and is just there for flavor, or 3. Pathfinder is just naturally easy and I should add more difficulty to the encounters?
Any reply would be helpful!
That's a pretty "weak" encounter. Altogether that's maybe CR 1. Worse, the crows aren't much of a threat, since it's not natural for crows to attack if they're not being directed to do so. A spellcaster could have taken the whole bunch out with a single 1st-level spell.
For CR in general, it's hampered by a lack of clear goalposts. There are goalposts for some stats by CR: hit points, AC, high/low attack bonus, high/low damage, primary/secondary save DC, good/poor saving throw. For a CR 1/2 creature those values are 10 hit points, AC 11, +1/+0 to hit, average 4/3 damage, save DC 11/8, and good save +3/bad save +0.
I don't know if I've ever seen a CR 1/2 creature with stats close to that. A 1st-level orc barbarian, a CR 1/2 creature, has an attack bonus of at least +4 to hit (15 Strength +2 from racial +1 BAB, so +4 to hit, before rage, giving another +2 to hit) which is 3 to 5 points above the curve. It will also have about 14 hit points, not 10, and that's before rage. The monster math doesn't make it possible to match the goalposts. Then again, finding a starting PC with an AC of only 11 is pretty rare. (First-level wizards have spell-like abilities, so can afford the spell slots to cast Mage Armor.) Those stats aren't really all that adequate, either. A good save is +3, but the starting save DC is at least 13 and probably a lot higher (starting stat 15 + 1st-level spell gives a save DC of 13, but a starting stat of 16 or even 20 is much more common, so save DC 14 or 16!).
Making matters worse, many secondary stats aren't given goalposts at all. Touch AC, CMB, CMD... it's trivially easy to have a creature with a nearly unstoppable CMB for its level, or one with an incredibly low touch AC, leaving them easy fodder for gunslingers.
And to top it all off, Pathfinder PCs can be markedly more or less powerful, both within and between classes. CR is just a very rough guide, less about "level matching" and more about "this monster is more powerful than that monster".
Once you have an idea of how powerful your PCs are, you can tweak encounters upward. Most APs aren't built with optimized PCs in mind (optimizing not just builds but tactics) and so you often need to beef up encounters. Three hobgoblin warriors might not have been much of a match for the PCs if they were bunched up. (A sneaking rogue could probably kill one during the surprise round, a wizard could fry at least one, a fighter could laughingly squish one...)