Leave your weak stomach and keys to reality at the desk, folks...
Without hesitation I have to say that the Astral Plane and Shadow Planes are essential, a part of the game I simply love, as I have been long waiting for a game that can transport me to such places. I find those places extremely intriguing and in general I like the darker theme to the game. I enjoy how characters aren't just plopped into a tangent, but continue on an epic story continued from the base game. I enjoyed the tale of my own adventures and I could not have chosen a more interesting part of Forgotten Realms lore than that of the Illefarn and the Netherese on the Sword Coast.
Fortunately the game continues that tale and involves the players with compelling cinematics and a very engaging plot which forces them to unravel several mysteries regarding a centuries-long struggle and a plague which the player must learn to manage for their very survival, enabling powerful abilities with strikingly-bold ramifications.
The player has been cursed with the ability to consume spirits in the form of a curse, an entity which must be fed such energy and mitigated, so that the player continually finds himself compelled to find and consume spirits unless he can control the hunger and develop the ability to channel it to purposes other than what is ostensibly evil.
I have to say I like the Spirit Eater aspect of the game. I have heard criticism and complaint of how it is an inhibitor and a real constraint, but I found that it was a very compelling feature and complemented the story very well. Other abilities are available for development throughout the game, all of which I found quite enjoyable, particularly the ability to Dream Walk. Altogether with the mystery that becomes a quest for survival against many elements of danger, and with a very appropriate and inspiring soundtrack, I found myself in effect dangling from a precipice below which yawned a terrible void of danger and alien nature in a sudden struggle for my character's existence.
The Shadow Plane is represented in fantastic and eerie gray-tone, where color only exists for magic, and even then it is dulled. This colorless world with its drear music tracks combined to give the very convincing feel of deep shadow and mind-rending despair. This was one of the parts I liked best about the game, though most of the other environments had a similar brooding feel and theme including the music, so that without knowing better one could lapse into a sort of nightmare limbo wondering why the very Shadow Plane and its gloom and menace seemed to bleed into the material world, as if the shadow and evil was encroaching on the world. In all it served very well for a character that was haunted by grave circumstances and very few options.
Of course had this been merely an adventure game or an action title, it would not nearly have been as enjoyable, but once more the D&D universe comes to save the day with a marvelously-interactive journey to bizarre dimensions and through other-worldly encounters chasing a deep and dark mystery with grave and horrific consequences for failure. At its heart is the same D&D RPG mechanics, a game involving adventure and action with gusto. Together with the stupendous and compelling storyline with breathtaking scope, I can give this game the praise few other games can earn for an umber and visceral journey into bizarre, wonderful and terrible worlds. This game vividly brings to life a darkness and evil that can be contemplated in few ways more convincingly than I have ever seen in a game.