Go back to '03 and look forward and try to find anyone who defended Anakin's fall or killing the kids in the temple. There weren't any. The whole fall, while we all knew it had to happen, was handled just terribly.
That said, we were never given 30 years of hero Anakin of which we were told nothing before he fell either. And it was a single character.
Sure, inflated expectations are a bit to blame - but 30 years down the road and all they can do to ANY of the OT characters is trash them. Everyone essentially regressed to the same point they were in when ANH started - or worse.
Han and Leia - we see nothing happy of the marriage. We're brought to divorced, Don't talk much, no one believes leia except a tiny band of resistance, han gave up and was doing lame smuggling. What we are told that happened to them positively the last 30 years? Nothing. Presumably they were married and had a kid. All we know really is, they had a kid who gave them both the middle finger and turned evil.
R2/3po - relegated to largely gathering dust in a corner.
Luke - quit on the galaxy, hid in the middle of nowhere, and gave up on the galaxy, his family, the jedi, etc, because a student turned evil. Never mind the fact he was the only one in the galaxy capable of facing that nephew. "I quit, let the evil win'.
Seems like Chewie was the only one not screwed over because he got a stronger blaster. Though he did have to go back to being a lame smuggler. He was honoring his debt so, the bad luck wasn't so much on him. However, when Han dies, someone he doesn't get the Falcon, it goes to the abandoned girl they've known a couple days who's not really connected to anyone, so, i guess they screwed him over too.
And before anyone jumps in about the books - that's a fail of logic quite frankly. A very small percentage of people who watch these movies are even aware of them, let alone read them. So, it's really not logical to say they all had lots of positive exploits, just read the books. Maybe 10% of the ticket buy crowd were in a group that read them. And that's being generous i think.
Lucas didn't tell anyone to read multiple books and comics before ANH premiered to get up on the story. The ST should not required the same thing either. Not even close. There were plenty of ways to respect what came before and make a set of new characters carry the day - they elected to stomp on it and set up the new ones on the ashes of the old ones. It wouldn't have been hard in the least to have treated them much better and pushed them into positions of power, retired, or died in the past. But no, had to go the belittling route.
That's where the break comes in, and where a good deal of the dislike comes in. No one expected 7, 8, or 9 to feature the OT crew kicking ass and taking names. They also didn't expect to see them wasted and diminished either.
Yoda wasn't a feature or focus of the prequels, but he wasn't treated poorly either. Same with Windu. Mon Mothma wasn't a remote focus in the OT, but wasn't treated poorly. The OT characters could easily have filled those roles or been left off all together. Hard to imagine them being treated much worse. If Lando shows up in 9 I worry he'll just be getting out of jail after a 30 year stint or something. R2 and 3po have to get obliterated, too. That's about all that's left.