I never felt cheated out of a raiding experience by not getting to raid Sunwell, but when patch 3.0 hit I did feel cheated out of getting to raid BT. There were a few people that were excited saying things like "Yeah, 6 progression kills in a night" but it wasn't really progression. We didn't have to craft gear for Shahraz or learn the mechanics of any of the fights we were steamrolling through. I didn't feel excited like "ooh, I get to kill RoS", the aesthetics throughout the raid were pretty much the same, I was underwhelmed at the prospect of getting free gear after working so hard to get the gear I had.
I say this because last time I came here talking about how awesome Ulduar was, people were quick to defend you, "So you want them to double the amount of raids they make? Impossible, etc." but that's exactly what you've done. You've brought your raid encounters to many more players but, I would argue, you've gone the wrong way about it. Now with LFR and Flex and Normal and Heroic versions of every raid you make, you've dug yourself much deeper into that "there's only so many hours in a day" thing. Now there's that much more focus and testing on (pretty much) the exact same encounters.
The reason that Ulduar was so awesome was because if you wanted to do a Heroic mode, it wasn't as simple and heartless as a few clicks on the UI, you had a guild discussion about it, it felt as if you really handed players the reins on how to raid. If you went for Heroic: Steelbreaker, it wasn't just more damage and an extra dps mechanic or two, the entire dynamic of the fight changed fairly drastically, and that was cool to play.
Now it seems that you're saying "Play our raid the way you want to play it." but with those types of challenge mode mechanics it felt as if it were "Make our raid yours", there was that extra level of involvement in choosing how to kill someone. I'm not saying that's the only route to go, but it seems like that type of innovative design is dying for the sake of increasing accessibility.