Their offense is mediocre; they lack a run game and their receivers are inconsistent. Andrew Luck and T.Y. Hilton look to be a great duo for years to come already, but their weak offensive line will hold them back until it's fixed. Their only solid pieces in the line are Castonzo and Satele (who's a Fin's reject). If Fleener and Allen live up to their potential, they should have a good if not great TE duo to help Luck develop, but so far Fleener doesn't look worth the pick. (again time will tell (*Michael Egnew should be held in this regard too))
If you notice, the games they won were all reasonably close, with margins of: 3, 3, 4, 6, 17 (woo!), 7, 2, 4, 7, and 12. Seven of their wins were by game-winning drives thanks to the heroics of Andrew Luck, who I might mention, is considered the top QB prospect since Peyton Manning. Not every team is lucky enough to replace a Hall of Fame QB with a #1 overall pick. When it comes to their losses, they were by margins of: 20, 5, 26, 35, and 12. Almost every time they lost, they were getting their as*** handed to them on a silver platter.
Honestly, I could see the Colts taking strides backwards next year, not necessarily Luck or the young receivers, but I think the O-line and D-line are going to cause too much trouble for them to make the playoffs again.