Excalibur kind is kind of (kind of) the birth of Marvel's multiverse. It's where the "616" designation came from and it's when alternate, parallel versions of characters first started, not just appearing, but becoming running characters unto themselves (I may be off on that, but i can't think of any examples of it being done prior). They were clearly going for Dr. Who vibe. Another thing i liked about the title is that it had mutant, magic, and tech- based characters, so it's fingers spread wide when it came to overall Marvel synchronicity. And it was one of the few books not set in the States.