Tilt is worse for the beginning books in the series but gradually gets better in the middle. The books towards the end of the series don't have much of a tilt at all. Please note this is not a crease mark but rather a slight bend.
Otherwise books are in clean, excellent condition. Covers have some occasional light scuff marks or scratch marks (examples shown in photos), and light weathering to edges and corners but overall look great. Issue 13 had the worst markings that were found, small scuff marks going along edge of spine (shown in photos).
Overall a good, clean, readable and collectible set.