This was my first introduction to this series, and it's the second book, so most of the introductory stuff has been taken care of. Erik Hinkle has a magical stairway leading to the world of Droon in his basement. When he and his friends all have dreams about the magical world, they know that the staircase will be open for them to travel to a new adventure.

They soon find themselves helping their friend Princess Keeah sneak into the realm of the evil Lord Sparr to retrieve a magical stone.

The format here is a bit like Mary Pope Osborne's Magic Treehouse series, except that the destination for the magical travels is an original fantasy world. This leaves a lot of worldbuilding potential, some of which works well, and other of which results in a species of sentient cushion-people. 

The action is fairly good, but I felt like the character development was lacking. Erik and his friends Julie and Neal felt pretty much interchangeable, without much in the way of personalities, and wizard-mentor-figure Galen Longbeard is about as generic as you can get. Keeah, and, somewhat surprisingly, the villain Lord Sparr, are a bit more interesting, although Sparr still resorts to yelling things like "Seize them!" more than anyone written after about 1980 should. The best character is the witch Demither, who has been compelled to serve Sparr, and who will hopefully get a lot more screentime in future volumes in the series, as she appears only briefly here but still totally steals the show.