For anyone who tried this last week the answer was given as O. The letters of the alphabet that contain only straight lines alternate with the letters that contain only curved lines. (I arsk you!!) However, surely T should follow O in that case?
Not very satisfying though is it when you are trying to be literary?
I would never have thought about looking physically at each letter as word puzzles are suppposed to be about your knowledge of how to use the letters not what they LOOK like!
Agree with TydFan, in common with numerical sequences you would expect there to be a logical progression, rather than a visual link. This type of sequence should perhaps be applied only to sequences involving shapes/patterns.