I'm not very versed in Blue Rose, but I do know that some of the larger differences are:
1) Escalating Toughness. Blue Rose Toughness saves go up with level, True20's do not.
2) Arcana/Powers. In Blue Rose, one buys a magical Talent as a feat, then individual powers in it two-to-a-feat. In True20, one just buys powers one-per-feat.
3) Skills. Blue Rose has a somewhat more complicated skill system, with the equivalent of "in-class" and "cross-class" skills, and the possibility to have a skill at half-ranks.
"All right, I am not the Shadow. You have nothing at all to worry about. Except, oh, wait, I'm pointing a gun at you."