A new review for Grand Tribunal is now up at RPG.net. Reviewer Shannon Appelcline says, "it shows its pedigree well: its plays and feels like an Ars Magica-based card game. Beyond that Grand Tribunal falls into the European style of play (meaning it has elegant, relatively simple mechanics) with American stylings (meaning that you can cause real chaos to your opponents with certain cards)."
Also, the RPGnet Gaming Index now has a complete list of Ars Magica products and a checklist page. If you're logged into an RPGnet forum account, you can mark ownership and ratings of every game. (You'll have to click through from that page to mark ratings of items with multiple editions.)