We are now mostly done with #3. The PCs have muffed escaping from the Cathedral with prisoners and are now going to have to fight a whole lot of giants. I believe they will win it, though.
#3 seems severely underpowered. For example, there's an encounter with a CR5 and five CR3 opponents one room before the purported final encounter. The PCs are either 9th or 10th by then. This is not even a speedbump. The enemies have nothing but melee and have trouble hitting the PCs. (My player spared me this fight by Bluffing through.)
The crossbowman with tanglefoot arrows can mop up giants in the open. Tanglefoot is a no-save slowdown preventing the giants from closing effectively. They can't hit at range. Ironically, the AP's deficit of places to shop for magic items set me up for this: he could not find any big magic items to buy, so he bought 60 tanglefoot bolts instead, and really nothing could have been better!
The psychic with confusion can win giant fights single-handed: confusion, vanish, eat popcorn while watching the giants fight. Hold person, slow, and even color spray are also highly effective, as is entangle when outdoors. Note that only one of these is a "person" spell so the defenses against "person" spells are not sufficient. Toppling or dazing metamagics (used with magic missile) are also outrageously strong, so strong the player deliberately removed the feat from his character after one session. He also removed damaging entangle. Giants' reflex saves are almost as bad as their will saves.
My player graciously gave me a party with minimal invisibility and no greater invisibility: the giants are unable to deal with it, except for a small number of ones with animal pets.
On the player's request, I wrote up rules for breaking the morale of the giant camp in #3 based on the ones in #4. I don't really recommend this as it will make #4 feel repetitious. I don't think they are working anyway. The camp is well centralized and the PCs don't have invisibility: their optimal strategy is just to kill the giants piecemeal until they have "accidentally" killed enough leaders to break the camp morale.
The player is talking about abandoning the AP as it's just too easy. He is running only 3 PCs, not terribly optimized, and he's a player who enjoys low-challenge games, but not this low-challenge. I have been giving the giants a bit of help here and there but I didn't sign up to rewrite the whole module....
I hope #4 is better.