Yeah, Willem Dafoe has a little cameo, not as grand as his last one, but he appears in the mirror again. Oh, and you know how the opening credits of the 2nd movie summed up the first one in comic book form? (I love how they did that.) Well, the third one retells both movies in the opening credits through clips and his "Avenge me!" is there as well.
Yeah, I rolled my eyes at the butler scene. I just don't get it. It's stupid.
And as to if the end of the movie wrapped up the Peter/MJ/Harry storyline well... I'm gonna go with no. I felt like there was a lot more that could have been done, and it was too nicely wrapped up.
I don't read the comics, but thanks to wikipedia I know a good amount about what goes on in the Spider-Man comics and I find it odd that they had MJ from the beginning as Peter's love interest, even though Gwen Stacy was actually his first girlfriend. And didn't she die horrifically and it was unclear whether or not it was Peter or the fall that actually killed her?