Release date: Officially Spring 2003. The Player Community has reason to suspect March 2003
Developers : BioWare and FloodGate Entertainment
Plot : In the Forgotten Realms there was once a nation of powerful wizards called Netheril. So great was Netherese magic that they lived in massive cities that would float through the air. Unchecked ambition destroyed their civilization and sent their cities crashing into the ground. Generations later the ruined cities are still filled with powerful magics and fell beasts. Undrentide is one of these cities.
Story: The story opens in the town of Hilltop near the Nether Mountains with the player uncovering a situation involving artifacts stolen by Kobolds for some mysterious reason. Help uncover the mystery behind the theft of the artifacts, then find yourself engulfed in an epic adventure to protect the citizens of Hilltop and the Forgotten Realms!
Number Chapters/Hours: 3 chapters with  30-40 hours of gameplay
Toolset Improvements: New wizards, voicesets, and scripting commands. Improved AI and inventory control for henchmen.
New Monsters : Basilisk, stingers (the monster to the left), Medusa, Cockatrice, Sphinx, Female Fire Giant, Gorgon, Wyrmling, a couple of new familiars (maybe a pseudodragon) and an animal companion
New Tilesets: Winter version of the rural tileset, plus a new desert and ruins tileset. Also new background tiles for existing tilesets.
New Music: Shadows of Undrentide will have new ambient loops to accompany the tilesets.
New Feats : Over 30
  • Divine Might
  • Extra Music
  • Bullheaded
  • Great Cleave
  • Dirty Fighting.
  • Zen Archery
  • Circle Kick
  • Greater Spell Penetration
  • Blind Fighting
  • Rapid Reload
  • Improved Initiative
  • Spring Attack
  • Bullheaded
  • Snake Blood
New Spells : Over 50 including the Bigby's hand spells and Petrification.
  • Acid Splash
  • Aura of Glory
  • Blood Frenzy
  • Drown
  • Inflict Critical Wounds
  • Inflict Minor Wounds
  • Magic Fang
  • Shield
  • True Strike
  • Quillfire
  • Displacement
New Skills : Tumble, Appraise and Hinted at a craft skill
New Prestige Classes : Yes, five.. Harper Scout, Blackguard, Assassin, Shadowdancer, and Arcane Archer
New Gear : Boots of Tumbling, Arrows of Petrification, plus powerful sets of armor and weapons wielded by legendary heroes. Grenadelike weapons, bandoleer of holy water, Choking Powder, alchemist's fire, or caltrops.
Screenshots:

This shot shows off the new desert ruin tile.

This is a shot of the new formions as well as another view of the ruin tile.

This shot is similar to the above two. Notice the well tile in the background.

You can see a new spell effect in this screenshot. We don't know what spell it is for, but it sure looks cool!

Here's another nice spell effect. This is probably a protection spell of some kind.