One thing I like in gaming (and perhaps it's the author in me) is the fact that characters are not merely the sum of their numbers. This is particularly true with ex Miscellanea. In my somewhat limited experience in creating members of different houses (I've played Bjornaer...quite a few Bjornaer, and an ex Misc, and will be creating a Flambeau this weekend for a new saga), I've decided that a good ex Miscellanea is possibly the hardest house to create a character for. With other houses, you only have to create your character, maybe some backstory, thumbnail sketches for your pater/mater and the covenant you grew up in/were apprenticed in. For an ex Misc, though, you need to create (for all intents and purposes) a new House with every character. Take a look at Fiona, over in JL's Ruins of Bibracte saga. I had (maybe not had, but felt the need to) flesh out her Tradition, the Daughters of Circe. Took a basic concept, did a little (Wikipedia-based) research, and came up with what seems to be a viable, if small, ex Miscellanea Tradition that has had a part in shaping not only the way I built Fiona, but the way I advanced her.
I used to have a superhero rpg called (I believe) Golden Heroes, came out in the early to mid 80s. Character creation mechanics were, for the most part, pretty straightforward and typical for its time: randomly roll the character's characteristics, powers, and abilities. But Golden Hero threw a wrinkle into it that stuck with me: you also had to come up with your character's origin and background on your own – no random table for it. And any power or ability that you could not justify in your character's origin, you did not get to keep. That mechanic stuck with me, and it's one I try to stay with in every game I play. The need to justify, even if it's a throw-away phrase somewhere, everything that's on the character sheet.
Now, with that being (finally) said, my rule of thumb is that I tend to be more flexible with stuff in char-gen if the player sells it. It needs to be more than "I think it would be cool if my magus had blah-dee-blah-blah." It should be along the lines of "My character has Mythic Herbalism because her tradition, going back thousands of years, has been particularly skilled in herbalism, and found ways to transform the minor magical abilities found in every living thing (in this case, plants) into something vastly more potent...something that can kill or heal a man, or something that can give whoever imbibes the transformed plant incredibly sharp vision". Something like that.
What I feel like I'm seeing so far, and granted it's still relatively early in the char-gen process, is some thought of motivation, of how and why his Tradition has certain things, but still a bit of cool-factor that we're trying to get hammered out.
For example, while I can see (from a real-world perspective) the appeal of immortality, the ability to not ever have to deal with the uncertainty of just what's in the Undiscovered Country. But in Mythic Europe, where the Divine is real and active, that should be less of a factor. People of all the Abrahamic faiths know what fate awaits them if they're saved Christians, devout Jews, pious Muslims, or what have you. And they know what they're sacrificing by turning to Diabolism (for example), but have convinced themselves that either the trade-off is worth it or that they will be able to find a way to get out of the fate they've chosen for themselves.
I'm having a hard time seeing why the tradition is seeking immortality, beyond the "I'm an immortal...being immortal is cool" factor. Why would a devout Christian seek immortality, knowing that if he found it, he would never be able to enter Heaven and spend eternity in the glory of God?
Perhaps the tradition all belongs to a religious sect that doesn't believe in an afterlife? If so, how does that color their tradition in other ways?
Anyway, it's late, I've got work in the morning (which sucks on multiple levels), and I'm rambling.
I'll try to be more coherent tomorrow.