I cannot think of any age group that this isn't perfect for. I'm a 29 year old college graduate and I've learned things from this yet my 4 year old cousin understands it and Aunt has been using it in her classroom since I introduced her to it. The songs are well written, articulate, and catchy enough that you'll be singing along within a few listens. I don't ever see myself tiring of this and strongly encourage parents and teachers to use this as a resource for teaching their kids. The band are also really nice guys and sent me a care package when I was in the hospital for surgery and couldn't attend their show on the same day.
What's great about it: Every song is good. Every video is good. A perfect way to learn.
What's not so great: Nothing's wrong with this at all.