I've done the Merry Mayhem, PaintmeJudy mysteries and Bonnie Hunter mysteries. Merry Mayhem is usually a one day mystery, i.e. New Year's Day, Superbowl Sunday and I would say qualify as beginner friendly and usually have larger pieces. Loved all of Judy's mysteries (you can still find them on the board).
Love Bonnie Hunter's mysteries. Her quilts, while they do have lots of pieces, she tends to break down the blocks in manageable sections for each clue. I have trouble with scrappy myself, (but I am learning) so for the past mysteries I've used at least one constant color to give me the "control" to make myself comfortable. As other's have pointed out, you don't have to use her color scheme if it doesn't appeal and you can just do enough for a few blocks (think table runner/topper) until you are sure you like the design. Or rather than scrappy just use single colors...it's your quilt you can do what ever you want! It's a great way to reach out of your comfort zone and pick up some new skills.
There is already a thread set up under Quilting Board Challenges, and if you do a search you will find prior year postings as well. I am lucky that I have a LQS that has an open sew on Friday's some of us will be getting together to work on it together.