I heard a lot about Shadows Angelus long before I got directly involved in it—even to the point of sitting in on a game session. The thing is—it was full, and I resigned myself to missing out on the 'best rpg EVAR.' Then, a miracle occurred... there was an opening, and Ross invited me to fill the vacant slot.
Stepping into an ongoing game with a complex, fully-realized setting was a daunting task, and I didn't have a character concept ready to use immediately. To make sure the new character fit in well, I ended up collaborating with the GM on my character design to a much greater degree than usual. The result was possibly the most interesting character I've ever played. Although I was only in the game for eight sessions (17 thru 24), during those games, and the blue-booking in between, I learned more about character development than I had in many other, much longer games.
The two things that impressed me the most about Shadows Angelus, in broad terms, were the world-building and the story-arc of the campaign as a whole. The Shadows Angelus setting is populated with NPC's we (the players/PC's) actually cared about, locations we wanted to revisit again (or in some cases, NEVER again!) and memorable details that brought the setting to life. The story arc for the campaign was well-crafted and executed, in terms of both the short (usually 3-session) stories and the final 'showdown' that the campaign was building up to. The plot was clearly 'going somewhere' and it all hung together quite well.
I also learned a lot about campaign design from some of the decisions that Ross made at the outset of Shadows Angelus. All our characters had a reason to be working together, to be involved in the story, and they all had clearly defined roles within the group. As a result of this, every character was easily worked into every session in some way—at least it looked easy. This was probably the most important idea to come out of SA for me—the thing that really made the game work so well.
That, and the best gaming group I've met. It wouldn't have been the same without you guys.