Storm of Zehir follows in the grand tradition of Neverwinter Nights (NWN) expansions in attempting to set its own direction and tone while incorporating portions of previous narrative to draw players into the history of the world in which the game is set. Like previous expansions there is much to love, and a little bit to hate about this expansion as it pushes at the boundaries of the engine and the genre.
A big difference between this expansion and previous NWN environments is the split between an overland map (where you move about an entire region) and actual locations in which you can move about. The overland map is wonderful for creating a sense of distance and ambiance, while the locations provide the depth necessary for combat, dialogue, and intrigue.
So as to get them out of the way, I will begin with the bad stuff. First and foremost Storm of Zehir has incorporated the dreaded 'random encounter' mechanic of D&D with the overland map critters. Because of the virtually limitless capacity for players to grind on overland critters the game was also built with the assumption that players would spend considerable time fighting cookie-cutter fights out in the jungle with 200 gnolls, 3000 kobolds, and a partridge in a pear tree. In my tabletop experience we have always avoided these kind of repetitive and functionally random encounters because: they are boring. Other players may disagree, as the wild popularity of MMORPGs might attest, but for me D&D has always been about story, and random encounters do nothing to move this along.
Secondly, the expansion has something of a split personality with regards to towns. Certain towns can be dealt with almost entirely in an overland map setting-- no loading required. But randomly and inconsistently, other towns require you to actually enter the town (load screen... load screen... wait some more...) and wander about. I would have preferred more consistency with when you actually had a town built in-game, and when you could access through overland text menus.
There are a few minor issues in addition to these two large ones, but by and large the positives outweigh the negatives. The first, and most gratifying, change from previous NWN2 content is the richness of the locations. Every environment is bursting with detail and objects; giving more of a feeling of a living world that players might recognize from Baldur's Gate titles, and less of the "our engine can only support 10 polygons on the screen at a time" of NWN [the first one].
Dialogue is also more satisfying in this expansion than previously, where unnecessary chatter has been reduced and useful conversation is more obviously there. Since this is an expansion, and not a game such as Baldur's Gate II, obviously the volume of dialogue is nothing to write home about. But what dialogue is available is tightly written, useful, or just entertaining.
Crafting has been improved in this expansion with the addition of 'recipes book' which can be directly accessed near workbenches to make gear. The mishmash nature of previous implementation has been cleaned up through a mechanic that has you open the recipe book, chose the recipe, and if you have the right components (many of which are simply gold costs now), viola, you make your item. The availability of crafting also reduces the dependence on finding merchants with items of the appropriate level and speeds up gameplay.
Finally, the last improvement I will get into is the story itself. Storm of Zehir builds on previous attempts with the old NWN expansions, and of course NWN2 in building a strong narrative that connects the various events of the core game, expansions, and Forgotten Realms into a story that sucks the player in and makes them feel like they are participating like they would in a real table-top game. As a DM my players always appreciated when their actions had implications in the world. When they built an inn and made a name for it, when they defeated the Dread Lord SomethingorOther and the townsfolk remembered it. Allusions to past events in NWN2 were well-placed and made me feel like I was really in a world where what I'd done previously mattered. I was proud of my Knight-Captain and happy to see her legacy lived on in some small part (with careful non-references to anything specific I might have accomplished...) I would love to see more expansions in NWN2, and have them all link in to each other in unobtrusive ways like this.
So in short, Storm of Zehir is a fun expansion that you will not dream about in years to come, but that you might mention to your friends. If you like NWN style games, or are a D&D fan this expansion is well worth your time. If, like me, you moved away from your D&D group and hunger for the experience of hanging out with your friends haranguing your DM and squeezing out some story from the teeth of tactical combat, Storm of Zehir is the best new diary substitute out there.