Ranked from biggest disappointment to tiny bumps:
When MP left DT and the subsequent release of ADTOE: The disappointment was so great, I couldn't listen to DT for like a full year.
Sonata Arctica releases Stones Grow Her Name: the only songs I liked were reworks or straight up re-recordings of their/Tony's old songs and it bothered me immensely, add to that a few absolute clunkers (I Have A Right, Don't Be Mean) and... yeah. I saw Unia in real time and managed to digest it and love it much faster than this half baked platter of mediocrity. Thank god they recuperated from that.
Daniel Gildenlow's years of meandering between Road Salt Two and ITPLOD: okay, to be fair, he spent a few of those years in a hospital, but starting from the split with Johan Hallgren, Pain Of Salvation couldn't do anything right for me. Sadly, the pattern continues - even though PoS published a great album, Daniel also unceremoniously fired the person who was responsible for a lot of the best moments on the album, and then brought Johan back and you know he's gonna leave again and when that happens I'll hate Daniel even more for firing Ragnar. Bleh.
Leverage releases new music (that I've been waiting for for 9 whole years), with a new singer who doesn't fit at all: None of you have heard about them so that's just me venting.
Kamelot releases their worst album yet, The Shadow Theory: ugh change something please!
Wintersun releases their procrastination save album, sounds like something Jari cooked up in his kitchen while panicking that people aren't buying his excuses about why Time II doesn't exist in the material world just yet: This was lame as fuck, just say the dog ate your Time II demos USB or something.
Fates Warning releases first album in nine years, is kinda bad: I didn't like Darkness in a Different Light, shoot me?
Amorphis Amorphising repetitively on The Beginning Of Time: If Amorphis ever went downhill, this would be the moment I'd pinpoint as the beginning of the end. Luckily they added some fresh elements back into their music and all has been well for 7 years and three albums.