I like ArM for the things it is. I like other games sometimes, as a relief, and have played others extensively in the past.
YR7 and others have mentioned their interest in what might be called "Ars Fantasia" - not something as different as the World Tree project (which revives and rewrites the game rules) - but something "using" the ArM rules, but different.
I'm wondering what that would be?
I think it is possible to do many things with ArM "out of the box", so the question is - What do you (or others) "mean" by an Ars Fantasia?
I am interested to start a thread to look into what "otherness" people might look for, changing some bits and keeping others. I have found that in most published games, the rules are substantially tied to the expectations of what will happen in game-play, and the background story/world should constrain what is possible so as to remain consistent with itself. (That constraint may be "anything goes" which is great, but needs to be said, and is actually pretty rare!)
Things I can think of where "DND" differs from ArM include (and so would raise as "is this what you are looking for?" and "why?"):
background world - ArM uses C13 Europe rather than a novel world, or a "generic" world. (Too many DND worlds seem to me to be "Generica". Europe lets one include huge amounts of detail to present an apprently "real" world to players.
monsters - ArM isn't usually monster heavy, whereas many games are teeming with monsters and monstrous combatstreasure - in ArM characters usually create treasures (in the Lab etc) rather than finding it lying aroundparty vs. community - ArM encourages a community of characters (the Covenant), rather than the Band Of Heroes
When I think of DND or many other FRP games I think of a small, fixed party (often 1-per-player), moving through a series of linked adventures one after another, rather than a broad community of dozens (or more), existing over years or decades.
They progress through a world which is "part of the game" - eg Forgotten Realms, Hyboria, Melnibone or Lankmar. The background of the world affects what is appropriate for characters to be able to do: ArM type magic might be fine in Forgotten Realms but be overwhelming in Lankhmar.
Fixed Parties of characters have special problems compared to ArM standard: you have to have something for all the players to do, so all the player-characters have to be (approximately) equally useful and "powerful". ArM as written makes Magi vastly more powerful than Grogs, and significantly more powerful than Companions. Mythic Companions can approach Magi, but still fall short. Most other games try to limit wizard and provide special features for "warriors" (and other mundane characters) so that they compete on "equal footing".
ArM games I have played have often downplayed combat and been focussed on character interaction, and problem solving. Other games I've played have often focused on "heroics" where the "Team" solve difficult challenges, often involving combat.
Other games often have characters threatened by hostile beings (monsters, enemies...) where in ArM it is usually magi who are the most dangerous beings around - magi may be friends or allies but when it comes to the dangers of the Haunted Forest (in our saga), the magi like to live there becasue the forest's reputation keeps out minor nuisances, and they can always make it a bit scarier if they need to; they may find problems in the forest, but they aren't scared of it!