This is because I've been kinda slow in reading Mysterious Flame but also because I can't make up my mind about it, and sort of wanted to wait until the end to make judgment.
But okay, might as well put some thoughts down now.
In workshop, they always talk about the importance of a driving plot/obstacle/challenge that is sustaining enough to move you through an entire novel. But then there was recently that thread we had over at Moonrat's blog on plot vs. style too.
My thing about Mysterious Flame is that I don't think that the book is very driving. Much of the book is about this guy looking through his old papers and books and comics to sort of find out about himself because he's lost his memory. The back copy of the book promises that he's looking for the memory of his first love, but this doesn't even come up until about 3/5 of the way through the book. While the history of all the documents is mildly interesting, it's not interesting enough to me to sustain my attention. I find myself growing weary, because every chapter is nearly the same - he finds some new boxes, pieces together a little bit more of his past, etc etc. At moments when I finally think plot is taking off, it settles again after only a few pages. The whole thing is sort of a plateau, and I think I'm not versed enough in Italian history and politics to care enough about how all the period pieces fit in. Don't get me wrong - it's not completely disinteresting, but I find that I keep turning pages hoping that there's going to be something that hooks me. I also think it doesn't help that Eco's style tends towards the verbose side. While he's a good writer, the way the plot is being doled out isn't sustaining me.
I'm about 100 pages out from the end, so I'll let you know how it ends up wrapping up for me. But so far, I'm wondering if I should have chosen Name of the Rose as my first Eco instead.