Phileasson's Secret is an expansion pack to Drakensang: The River of Time. It adds a new area complete with all new maps, graphics, voiced characters, enemy types, puzzles, side-quests, unique items and loot, and a fully realized storyline and quest line.
The quality of all the new content is excellent. The artistic look is a nice contrast to the main storyline and locations of The River of Time. The items and extra level points you gain in Phileasson's Secret will make the final battles in The River of Time easier. It will help with the Sunken Temple battle in The River of Time, which can be quite hard.
There is also an additional side quest that takes place in the main game river locations which is quite enjoyable and amusing. It's a simple side excursion involving some alley thugs and a treasure map merchant. Things get out of hand quickly and you'll find yourself battling ghosts in secret treasure caves.
The Drakensang series brings back the classic 80s pulp fantasy style of story. It's the kind of story you would read in a cheap 80s D&D paperback or in a serial fantasy magazine from the 50s-60s. That's not a bad thing. There are a couple story twists, and it's simply enjoyable without trying to be dark or grim. Heroes are allowed to be heroes. Bad guys get over-the-top cut scenes. Thieves and scoundrels are always likeable and there is always a full mug of ale ready for you at the inn.