It's awesome celtic music for free! And it's great. Drinking songs, sad ballads, bag pipes, flutes, drums, harps, songs of war, songs of love, established musicians, up and coming musicians and much more. If you can't find something here that you like then you may need to check your pulse because you might not be alive.
Seriously Marc puts in a lot of work to get these podcasts out and it's a great place to find new music or just listen your favorites. Heck he even played a ballad about syphilis!
There's even Celtic Workout music workout episodes!