The reason it works so well is that Trevor started with the question "why is OTR so complicated?" and began removing parts until he had the minimum. Then, he looked at that and built a completely different protocol that achieved the same goals but where every part mattered.

That's usually the sign of a good crypto design -- every bit of the message and computation is vital and can't be removed without everything else falling apart. Excessive round trips, duplicate fields, data sent twice -- these are all signs of a lousy design that probably has security flaws.