It so happens that I bought OtR/AS just a few months ago and played one PBEM game, and am currently playing an AF PBEM game, so I think that qualifies me to compare these games.

In a nutshell, OtR/AS is more complex than AF. However, I don't find the complexity excessive, and I enjoyed playing it. In fact, after playing OtR, AF seems kind of lame in comparison. Both games have turns and slips that can be executed after moving straight a certain number of hexes, and in both games there are speed losses associated with those maneuvers. OtR/AS does a much better job of integrating horizontal and vertical maneuvers, though. For example, in AF an airplane with a speed of 6 always moves 6 hexes on the map regardless of whether it's diving, climbing, or flying level. In OtR/AS, an airplane with a speed of 6 may not move any hexes at all on the map if it's in a vertical climb or vertical dive. Also, you can use vertical maneuvers to effectively tighten your turn radii or do a quick reversal of direction on the map.

OtR/AS does require a little more math to calculate net speed increases or losses. Although I haven't played it face-to-face, I would expect it would play slower that a comparable game of AF.

In OtR/AS, each plane rolls a 10-sided die to establish the order of movement for each turn. The advantage of tailing another aircraft is that, if desired, you can declare "tailing" and automatically move immediately after the aircraft being tailed. I works out a lot better than the lousy tailing rules in any version of AF/Dauntless I've seen. Also, ace pilots get beneficial die roll modifiers, etc. I think it works well.

I hope this helps.