I finished Stone Shield and RF, and now I'm playing Enemy Within. First one is quite simple and not very difficult, except maybe mission #7 and #12. Many missions start with the plane started and there is no JTAC interaction, inputting of coordinates, offsets, etc. It could be interesting for novices. After that one, I played RF and this is more complex but not too difficult. You have lots of JTAC interaction and objetives are well balanced. Now I'm playing TEW and this one requires advanced knowledge of aircraft systems and taking real time decisions as objectives are received in the air. When I finished I will start Piercing Fury.