(I bet alot of people bitched when CC came out that it was too different than WM)
Did they ever! It's hard to remember all of these years later with Marco's reputation as a sort of "metal god", that he wasn't instantly looked at that way when he joined Nightwish. Many people *hated* his voice in contrast to Tarja's. That was the biggest adjustment that I saw among fans at that time. Personally, I didn't like how when Marco got there how he sort of "took over" as the "mouthpiece" of the band in live shows. I felt at the time that really wasn't his place; he's the "new guy", you know? But of course, all these years later, it doesn't bother me anymore, and I don't really know why it ever did. But yeah, it seems that each new album that comes is a major transition for a lot of fans. Just as many fans (who may not have protested to Century Child) didn't take as easily to Once, or didn't take to DPP. I've been a Nightwish fan for nearly 11 years and I've never seen an album come out from them where everyone is instantly on the same page and agreeing that it's great, or that it's bad. There are always those that take a long time to get used to it, or never really do.
But it's like you said, that's what's great about the band; every album is distinctly "them", but also very different from the ones before in their own way. I admit it took me many listens before Imaginaerum grew on me. There was just so much there to digest that it was impossible to start picking out favorite songs right off the bat, as I have been able to do with past albums. I think that's where many fans have had trouble embracing this album, because it's not something you can just take in small doses here and there, and that's not easy for a lot of people who have become accustomed to listening to music in a different way. Honestly, it took me back to the day when you listened to *albums*, not *singles*, and that's why it's a special album too.
This is probably a huge reason why a lot of fans have not taken to it as quickly; our musical experiences have changed because of things like the internet, so a lot of fans out there are too young to remember when you walked into a store, bought a CD (or album, in some of our cases), took it home and listened to the whole thing while studying the lyric booklet and looking at the artwork. Most people have become used to getting their music right here, right now, and don't have the patience to stick with something that doesn't grab their attention right off the bat. While there have been many advantages to the way music is listened to these days---such as being able to *find* these bands that don't get any exposure in our country---I think that is the biggest downfall too; people's attention spans have become shorter and if they're not blown away by something instantly, they write it off as not being any good. There are so many albums/bands out there that I didn't like on first listen either, and that I'm glad I gave another chance, because I would have missed out on some really great music if I would have let first impressions decide whether or not I was going to like something.