Hi, long time reader, first time poster.
I was very unpleasantly surprised with a few recent releases that are awfully mixed and/or mastered.
So here's my current top 5:
1. Duffy - Rockferry. This girl's album is very promoted over here in Poland, with lots of radio and tv presence (the single "Mercy"). I was wondering how this album would sound and... well... it doesn't sound any better compared to listening to the song "Mercy" on radio in mono.
In the first song, it's apparent that they used SO much dynamics compression on the singer's voice it's a pain to listen to. When she sings louder, the only thing that gets louder is the reverberation or echo in the background - sounds really, really bad.
2. Avantasia - The Scarecrow. Their previous releases, The Metal Opera part 1 and 2 were loud, but besides brick-wall hard limiting the dynamics were pretty much ok and each instrument, each singer had it's place. This new release is... well... tragic. A pure example of how to destroy music. I never listened to the whole album in one sitting. I always turn it off after the third track, which starts with a guitar, but when the rest of the band starts playing, instead of getting at least a little bit louder, it actually gets quiter. I could live with that, only if the sound quality was okay... but it isn't. The songs sound, I don't know, flat? The most fascinating thing about this album is that Tobias Sammet, the project leader, is very pleased with the production and said in one of the interviews that the band spent a lot of money to get "good" production...
3. Porcupine Tree - Fear of a Blank Planet. The production is pretty good in overall, but sometimes, due to the loudness war, the drums disappear below the wall of guitars. Thankfully, the DVD-Audio 5.1 mix sounds surprisingly well - and the drums which disappear on the stereo mix, sound very good: properly loud and audible. Steven Wilson even got a Grammy nomination for the 5.1 mix.
4. Antimatter - Leaving Eden. The album may not be as loud as other recent releases, but somebody totally ruined the drums. I don't know if it was during the mastering or during the mixing, but the drums sound... well, they just don't sound

You can achieve the same effect using hard limiting at, say, -15dB (I don't know much about audio production, but I like playing with audio editing).
5. Riverside - Second Life Syndrome. I don't know what the band and what the engineers were thinking. I also think this album is not as loud as other rock/metal music nowadays, but... everytime there's some keyboards and guitars at the same time, the drums fade out... it's extremely annoying - the drums' loudness is simply reduced by a lot when everybody in the band is playing at the same time.
That should be it