The tutorial appears to be built around Google's Blockly, and at first blush seems to be essentially guided tour of Scratch. After a few minutes playing around, I was so skeptical of its value in anything above a third grade, that I took it home and tried it out on my first grader. I had previously shown him Daisy the Dinosaur and Cargo Bot, neither of which did anything for him. Imagine my surprise, though, when he got into it. And I mean into it! He passed up on dessert and playing on the Wii because he wanted to keep doing it. (I'm sure the Angry Birds theme helped!) He needed a little help, but not much, and I thought, yep, suspicions confirmed, great for the younger crowd, but not ideal for a true intro for most kids.
Then, when it was time to turn it off, I accidentally ended up in the main menu of challenges and was blown away! My son had reached level 7 of what it shows to be twenty, in about 15 minutes. I figured that was all there was. Once I was in the main menu, I could see exactly what this game/tutorial had going for it.
Hour of Code is a solidly put together piece of software, comprising 20 total levels, most with a significant number of sub-levels that runs through a substantial number of the underlying principals of code theory, from if and if/else, to while to functions with parameters. In addition, the game play/learning is a repetitive looping technique, where they practice a skill several times to get comfortable on it, are then asked to use that skill and incorporate it with a new skill that they are learning, and then come back to this first foundational skill, and are asked to expand upon it. There is quite literally something in here for everyone. I highly recommend getting this into the hands of your students, even if it has nothing to do with your subject area; find any excuse. Let it open the door and they can take it where they want to from there.