Mind Flayers and Epic Levels and Robes and Skies. . . Oh My!
Hordes of the Underdark is the best of the expansions delivering not only additional content for the game, but also delivering a Neverwinter 1.5 experience. Additional content not only included a new single-player campaign set within the bowels of the dangerous Underdark, but also technical add-ons for previously created single- and multiplayer experiences.
With the addition of Epic levels your custom created character could advance skills beyond the traditional level 20 cap. With additional powers, skills, and feats heroes could hope to defeat the horrible opponents in the Sunless Citadel. New opponents included the dangerous Mind Flayers, all-seeing Beholders, and other denizens of the Underdark. Many of the new models looked impressive and clearly outperformed the blocky, old models (such as the Troll).
With the additions of items, creatures and some performance tweaking, the minimum system requirements were increased. This was necessary given the visual upgrade and environmental fine-tuning which took place under the proverbial hood.
With the inclusion of the Aurora toolset in the original Neverwinter Nights release, customization created an enormous grass-roots community. The additions to that community increased in predictable and beautiful ways. Character customization got a shot in the arm with additional armor, weapon, and body types. Multiplayer servers everywhere carried new lines of wearables (including robes), and reported new races in their census. The camera was unlocked to allow players to pan down from a high-level perspective to a ground-level view. This then allowed players to witness the awesome sights of true Neverwinter Nights in the Neverwinter sky. Sunsets, rain, and starry skies were visible for all.
In an ideal world many of the improvements of HotU would have shipped with the initial release. Nevertheless, the modifications are better late than Never.