I love In Nomine, but even I will admit that the system...the system makes tiny puppies weep, and not in a fun way. The concept is a cool one, and with chargen level celestial characters, it's reasonably okay. But it doesn't scale up well, or down well, despite both of those being offered options. The Words (the factions your characters can belong to) are badly unbalanced based on how cool Pearcy thought an NPC was, which can make for a very uneven party. The core book has the worst organization I've ever come across, and some of the rules don't make sense...Disturbance rules are messed up (especially for distances), the effect of Roles on Disturbance is...badly and inadequately explained. Some resonances are not explained completely (Such as the response a Mercurian gets when resonating a character with a Role), or are badly explained. Combat rules are sketchy and incomplete: there are no rules for choking or grappling, and you've got a better chance of doing damage with a set of brass knuckles than with a gun.
That said, it's actually a lot of fun to play...just be prepared to have make up a lot of mechanics on the fly, or occassionally just stop and say, "...no, wait. That's dumb. We'll do it this way."
Nobilis, actually, I think. The architecture of the setting really begs for there to be some kind of central GMing authority. You could run IN with Capes, but everyone'd need to be on-board to maintain the flavour. PTA might work, but I'm still working on the way to design characters with a bit of detail and texture.
I don't have Nobilis or In Nomine to compare notes... but from what I do know of IN, I don't think Capes is a natural fit due to the shared universe aspect.
That said, it's actually a lot of fun to play...just be prepared to have make up a lot of mechanics on the fly, or occassionally just stop and say, "...no, wait. That's dumb. We'll do it this way."
Capes or PTA?