If you are looking for a commentary that provides depth, knowledge and understanding of the Gospel of Mark you will gain an excellent contribution to your library. The commentary provides some great Greek information as well as from the LXX. I would say that if the person is desiring to move from the lay mentality to the scholarly this is the commentary to help in that process.
This was my first commentary on Mark and it's the one I always turn to first when needing consultation with the text. Lane is a trustworthy scholar who helps make sense of the Mark and brings deeper truths to the surface. This commentary - though not as technical as others - is very pastoral and offers deep insight into applying the text into the real lives of people. This will be a continuing treasure in my library.
Lane discusses the critical along with his more conservative views with proper balance. For Greek study I would also use the NIGNT entry as well. Overall this is an excellent resource for those who want a thorough study of the topics in Mark.
Lane's brief history of the book is also quite informative without being overly verbose. A good read as well.