I played Endless, Nameless expecting an old-school text adventure, and I wasn't disappointed. It's a text adventure, wrapped in interactive fiction.
It starts out simple: you are the hero in a game called Nameless Quest (formerly known as Endless Quest) and you have to rid the land of an evil dragon.
You have to solve puzzles to learn magic and to get weapons. They are generally hard, but logical, and asking for hints is encouraged.
The story might seem a bit thin at the beginning, but slowly expands as you progress in the game, which I found very intriguing. You're not only working towards your quest, but also uncovering a greater mystery; and without spoiling too much: dying is important, and the game is quite meta.
I especially liked the writing, it's humorous overall and manages very well to create a fitting atmosphere.
All in all, I'm extremely impressed by Endless, Nameless. It's a great synthesis between puzzles and story, humor and mystery, between classic adventure and innovation. I've played it for many hours, hunting for easter eggs and finding all the beautiful and horrible endings, and I enjoyed every minute of it.