Anyone interested in purchasing 5th Edition might want to do it sooner rather than later, as they have a 25$ introductory price till December (at which point the price will rise - I'm not sure by how much).
I'm currently running a
PbP ArM game. We'll see how that goes.
I find that by nature ArM is less about combat then D&D, as the game has in-built political systems and considerations and is less "balanced". Combat tends to be more of a story element (either weak adverseries or too-strong-to-beat), as fine tuning the battle is difficult (no CR system, characters aren't balanced really) and often combat will be a very bad choice politically (harassing faeries, interfering with mundanes...). This enourages less combat, fighting only when it is truly necessary. There are no "wandering monster tables" provided in ArM.
I also find stories are harder to brew, as a GM. Historical issues keep nagging at the back of your head, so you research some history (which is fun, but time-consuming). And lots of familiar story-hooks don't work so well. The characters have a life, and you need to come up with an actual reason why they would risk it. They aren't suicidal adventurers, sigh.
On the up-side, you get to learn interesting stuff and have a more coherent life for the characters, which make the stories more meaningful.
Of course, your game is what you make of it. This is all just what I find ArM enourages.