It's certainly good for beginners who are looking to get into competitive programming. The problems can be somewhat challenging to someone not familiar with algorithms or computer science fundamentals I think. The code for solutions often isn't complex at all, but they typically involve applying some sort of algorithm to a made-up (often funny) real world problem. You're not building a to-do list app, you're writing algorithms.
It's sort of like a word problem in high school math. The math itself is often just addition and multiplication, the hard part is figuring out which math to use and which numbers to apply it to.
All of the old problems are on the CodeJam website though so you can go check them out and give them a go!