Let's get this out of the way first: Against the Giants (ATG) is the archetypical AD&D adventure. The three adventures comprised in this collected work were written during the period when Gary Gygax was putting together the Player's Handbook and the Dungeon Master's Guide. Reading through the module now is like reading the UR-manuascript which informs all future TSR adventures. Niether the composing adventures nor the compilation are flawless. However, the criticism presented below benefits from 30 years of hindsight and exposure to many products born from this work.
ATG is a high-level adventure for around 9 characters of 9th level. Given the monstrous challenges found in the halls of the giants, players can expect some attrition in their numbers. The setup is simple: giants have been raiding nearby human settlements. The rulers of these settlements wish this to stop. The mission presented to the players is straight-forward: hunt down the giants and, if possible, discover the reason for their incursions.
This setup is clean, without a cluttered backstory and provides sufficient motivation for the players. However, I am an unfrozen caveman dice chucker. More modern players may find the lack of backstory off-putting and the absence of a personal connection to the lives of the player characters to be a fatal defect. A crafty DM should be able to manufacture custom story hooks for those players who need a more personal stake in the giant raids.
There are three giant rulers responsible for these raids: the hill giant Nosnra, the frost giant Grugnur and the fire giant Snorre Iron Belly. Each has his own fastness which the characters must assault (in the order given above). Again, modern RPG sensibilities might be put off by the abrupt way in which the PCs are dumped more or less in front of each fortress. There is no wilderness component provided for in the text. There is no nearby town for supplies. The PCs are own their own.
As each chief is conquered, clues to the identity of a third party pushing the giants appears. If you do not know who this is, STOP READING NOW.
A crafty (and according to Gygax's own fiction, busty) drow elf named Eclavdra has pushed the giants to war with the humans. Perhaps my reading comprehension skills are failing, but I cannot understand her motivations for warring (other than she is eee-vil!). Perhaps the follow-on modules, D1-2 and Q1 explain this a bit more. In any case, that mystery is not explored in ATG.
I believe that ATG is the module series that introduced the drow elves, which is Gygax's take on the traditional "svartalf" of Norse mythology. Throughout ATG, Gygax leans heavy on traditional Norse folktales. He goes as far as to say that the fire giants lair is "in effect" Muspelheim. This isn't to suggest that the PCs are hopping around the Outer Planes -- that's a concept that had not yet been developed, I suspect. That the fire giant king is named Snorre must be a knowing wink to the author of the Prose Edda, Snorri Sturlurson.
As a creature, the drow elves would go on to feature prominently other modules through out many editions of D&D and associated fiction. While I have yet to play ATG, I did play Q1: Queen of the Demonweb Pits and so was introduced to the drow very early in my RPG career.
The monster challenges that appear in ATG could not be more iconic of D&D, starting right with the giants themselves. I believe the only type of giant that does not appear in the series is the very power storm giant. Dragons also make strong appearances, including the a Smaug-like red dragon sitting on the largest treasure trove I can recall seeing detailed in any TSR module.
I also enjoy that the kinds of monsters that plagued low-level PCs, like orcs, trolls and hell hounds, appear as almost slaves of the giants. That's a wonderful display of power differential that adds verisimilitude to the monsters.
The treasure, strewn about the various fortresses, is remarkable too. There are several intelligent magic swords, which ordinarily are rare finds. Could it be that Gygax wanted to make all magic swords unique creations? Possibly. This idea that all magic items should have a unique character is a popular meme in the current Old School Renaissance.
So much of the content of the adventure. There are some troubling production qualities to ATG that require some airing.
Firstly, the maps are not labeled. That is to say, at first glance, you do not know which of the three sets of maps is that of the hill giant's fortress. When these modules were separately published, this confusion did not appear. However, when the maps were collected into one unit, this user interface issue was overlooked. Each section retains the original introduction, which adds distracting redundancies. Finally, there is a short-hand used in the monster stats (just giving the HP for each) that requires that the DM have the Monster Manual on hand. I suppose most of us have all the rulebooks on hand anyway, but this requires additional lookups that are unwelcome.
Despite some production issues, ATG is a strong product and likely to provide hours of entertainment even to modern players.