OK, it's been a while since anyone asked me about my time playing Ars Magica. I came to the game late, having played one session in the early 1990's and been hopelessly confused, but then came back in 1999 with Fourth Edition and have been playing ever since. I have written on, I dunno exactly, maybe seven fo the book for the line that have been published so far, and I originated the Ars Magica fan convention Grand Tribunal that now runs every year, in the USA (normally California) and in the UK (either in Cambridge or Cheltenham).
Ars Magica is a bit of an epic game, and I'm guessing you have the basics by now. It's about magicians - members of the Order of Hermes. They are immensely powerful - not Nobilis powerful, or perhaps even superhero powerful, but their magic properly employed can level cities, make ships fly, cause great plagues and if they work in their labs they can construct magic items of awesome power. Unlike most rpgs the way you get better is not to just go out adventuring - it is to work for seasons, often years in your labs, studying, experimenting and investigating mysteries. You read books, you write books, and you trade with other magicians favours and raw magic stuff - called "vis" - for access to their libraries and grimoires. You can invent completely new spells, right from the moment you start, in an improvised kind of magic called "spontaneous spells". If you magi lacks the spell it needs to get across a river, you can improvise from what you do know.
I'll link to a little primer I made a couple of months back on how the magic system works later - the presentation is shockingly bad, but if you persevere with it I hope you will understand the mechanics of the tabletop rpg, and more importantly how to cast spells, which I'm pretty sure will be in the computer game.
I have run a lot of Ars Magica campaigns, or as they are called sagas over the years. These all dealt with a group of magi who live together in a tower, castle, cave, village, flying ship, among the clouds: you design this "covenant" yourself as a group at the start of the game. Covennats designed by my players as their magi's homes included
* Deep in the heart of an active volcano near Thera, an island in the Mediterranean off Greece. Their magic allowed them to here, just about, (mainly) safely protected from the lava! The game was a playtest for the Thebes book The Sundered Eagle, and was great fun. It's a very different setting in some ways, but the magc is the same.
* A ruined covenant destroyed in The Anarchy of 1154 in the Fens of East Anglia, England, where the players explored the ruins, rebuilt the covenant seventy years after it was destroyed and finally laid the terrible spectre of Geoffrey de Mandeville. The story took place over about 30 years of the characters lives. Ths was my post popular saga, and I would bore you if I talked about it!
* A high tower in the foothills of the Pyrenees, during the Albigensian Crusade where they took the side of the Cathars and protected them from the crusaders, changing history by preventing Carcassonne falling. One crusading army was destroyed by giant wasps conjured up by Benz of Tytalus with a Creo Animal spell, and others had giant boulders shrunk by magic, loaded on to leaves that then were made to fly by magic, and then both spells were dispelled once they were above the poor knights! This one lasted about 12 years, before we moved on to another saga.
* A castle in Normandy, they seemed to stealthily creep around the countryside in a weird blur each night: no one ever saw it move, but it was never in the same place when they awoke, wandering all over the Contentin Peninsula. The castle had a problem: it thought it was Notatus, apprentice of Bonisagus, an important figure in Hermetic history. (it was actually a powerful faerie, though Notatus had been imprisoned here once, perhaps). I think this one covered about 30 years of the characters lives.
* Within a regio, or sort of "pocket dimension", hidden within the stones of Avebury Circle, England. Only a few could find their way in and out, and those trapped within aged only on leaving, and hence some had been there hundreds of years after getting lost on the moors at night, but could never leave without crumbling to dust. The magi had no such problems, but had to deal with the pagan ways of the inhabitants.
* Most recently, St Peter's School, York is the setting for our game. The players built a flying ship early on, and were involved in defeating a rebel invasion at Dunwich and Fornham (1173), exploring the deserts of North Africa, saved Richard the Lionheart, found (and put back) the Holy Grail, prevented the Sac of Constantinople in 1204, defeated the villainous Guy of Gisburne in Sherwood Forest, found a unicorn to save the poisoned King, made magic items so deadly the Order is debating banning them, defeated a powerful Faerie Lord of Ice in Cumbria, averting a disaster, saved the Jews of York, discovered a legendary lost covenant, and last season were preventing the signing of the Magna Carta. They have done much more as well, but that is some of the higjlights. One of the characters, Lucius is now Primus of House Flambeau; a companion (non-magus) character Aleister DuMond went from humble school teacher to Lord of Carlisle, and the Redcap Paul fled the covenant with a fortune in magically created wealth and managed to buy his way to being the Bishop of Durham before the magi managed to get him excommunicated. The game has taken place over 54 years so far 1160-1214. The magi are aging, but growing in power, and some of the servant characters (grogs) and companions have died of old age or been retired, sadly missed until they crop up again needing help in stories.
Anyway a few links - here is my primer - http://jerome23.wordpress.com/2012/09/03/about-my-hobby-for-non-gamers-an-introduction-to-the-5th-edition-ars-magica-roleplaying-game/ - the basics of the magic system explained
This is really odd - we refought a battle using Ars Magica - http://jerome23.wordpress.com/2012/08/22/the-mythic-battle-of-fornham-1173/ - quite an achievement for any tabletop rpg system!
And there are reports on a few of the UK conventions for Ars Magica I have hosted here -
I can't speak for Atlas Games, but I can speak as an experienced roleplayer (I've run campaigns with D&D, Traveller, Call of Cthulhu, Pendragon, Golden Heroes, Unknown Armies, Nobilis, Feng Shui, Changeling, Vampire, Werewolf, Maelstrom, Clockwork & Chivalry/Renaissance, WFRPG, PrimeTime Adventures, Bushido, Over the Edge, Chivalry & Sorcery, Runequest, Heroquest, Elfquest, etc, etc) about how the system differs and answer questions if people interested but be better if more experienced players recounted their experiences with the game.
Hope mildy amusing