The Ivory Triangle is to Gulg and Nibenay as the City-State of Tyr expansion is to Tyr. Except that the latter publication was more original. The Ivory Triangle certainly contains a lot of duplication from other sources, all crammed in to the locale of Gulg and Nibenay.
Physically, this is a boxed set that contains three sources books (see image below), several maps (notably of the city-states of Gulg and Nibenay) and some expansions to the Monstrous Compendium. The main book is the one entitled the Ivory Triangle, whilst the other two, detailing the city-states, are comparatively lots smaller.
The main book kicks off by describing several forts (e.g. Fort Inix). This is nice for fleshing out locations and figuring out the kind of trade that occurs (cf. Dune Trader), plus some local NPCs, but is otherwise okay but but phenomenal (a repeating theme through the accessory). The next chapter concerns itself with raiding tribes, and to be honest: is not truly ground that wasn't broken with Slave Tribes: simply more details on tribes that you might like to run in the local area. The third chapter concerns itself with the lands of the Ivory Triangle - and this is where the information is good and new ground is actually broken. The sites of the ancient battlefields in particular is a highlight, but perhaps more "on-going" war might have been preferable to cover. The Crescent Forest is also entertaining as it contains surprises like a tribe of Halflings.
The other two books on Gulg and Nibenay are solid and provide a good deal of background to these cities (with some duplication from the adventure Asticlian Gambit, and the expansion Veiled Alliance). The highlight are the maps depicting the two cities, which are fold-out style in the same vein as the other campaign maps.
Overall, its 3 out of 5 from me for the Ivory Triangle. Lots of duplication from other sources really detracts from what could have been a good expansion set. If you need details on Gulg and Nibenay (and its surroundings), then this is a great expansion. But if you have many of the other expansions, and aren't particularly bothered about this region of the planet, then skip it. It could have been much more than it is.