"Grasping God's Word" is excellent! A great book to learn how to study the bible.
As for study guides, I develop my own lesson plans for each class but I've used resources by Ralph Wilson in the past. Check out
"JesusWalk" Study Guides.
As I look, he doesn't have anything for the gospel of Mark but you may want to flag the website for future reference. Much of his material is offered free on the website but can be purchased for a small price in printed form and even downloaded in bulk for Sunday School teaching.
Re: "
shallowness: or 'depth of teaching', the term can be misleading.
I tend to gravitate toward intellectual study methods but have studied under class teachers that are not so inclined and still learned a quite lot.
A teacher that teaches with emotion sometimes promotes relationship and change in a way that intellectualism just misses out on.
A study guide in the right hands can offer structure to keep a group on focus.
To each their own, that's why God made so many different church bodies.
Rob