I'll try this, chronologically:
1.
Linkin Park -
Meteora2003, one of the most important years for me when it comes to music.
I had already been a fan of LP since Hybrid Theory, an album that I could've placed here instead of Meteora, but I went with the latter. (kinda a tough call)
When Meteora came out, I was just blown away by how great it was, it had everything I loved about Linkin Park, and also added a lot of new aspects to their sound.
'Breaking the Habit' was a very artsy song back then, a song that stood out as a favorite on the album, even though it didn't fully click until later.
This was an album I spinned pretty much every day, I knew the lyrics in and out, I could sing along to all of the songs, and this was one of the first albums that I actually purchased a physical copy of.
Most importantly, this album made me interested in music, and it's kinda where my journey started.
2.
Iron Maiden -
PowerslaveA while after my interest in music began to expand, much thanks to LP, I discovered Maiden.
They quickly became a favorite, I kinda discovered them through friends, but also played a lot of GTA: Vice City at the time, and it had "2 Minutes to Midnight" in the soundtrack.
Powerslave became my favorite Maiden-album quickly, and still holds that spot today.
The title-track is probably my favorite Maiden-song, I played it on repeat for hours back then, even though I don't listen much to them anymore.
3.
Opeth -
WatershedAfter listening to metal for a few years, this was pretty much the album that got me into Progressive music.
I was blown away by the transition from Coil to Heir Apparent, and this album quickly became a favorite of mine, being more diverse then anything I had ever heard before.
This was almost at the same time as I discovered Dream Theater, another band that got me 'from' metal to other styles of music, but I went with Watershed for this spot.
Anyhow, this album was my first insight of Opeth, and even though I don't rank Watershed in my top3 Opeth-albums, it still holds a very special place in my heart.
4.
Anathema -
JudgementAfter getting more into Progressive music, I read about Anathema here and there, so it felt obvious to check them out.
Started with "Fragile Dreams" which was a fantastic song, and decided to start with Judgement, seeing as it was the most 'appreciated' album on lastfm.
This album didn't do much for me initially, I must have spinned the album 5-6 times before I realized it's epic potential, I have done the mistake of giving up on albums and such too early in the past (Frames being a good example), but Judgement took some spins to click, but when it did...
It was one of the most emotional albums I had ever heard, "One Last Goodbye" is a great example of a song that really created tears in my eyes, such beautiful and sad atmosphere.
This album is one of my favorites from Anathema, and it's just fantastic throughout.
5.
Sigur Rós -
( )This album stood out from the first listen as being like nothing I had ever heard before.
It's hard to explain how I feel about it, and it may sound pretentious as hell, but this album felt like it was really special, the atmosphere and the songs, it was just something 'out of this world' to it.
The haunting vocals of Jonsi, the beautiful landscapes and the 'theme' throughout the album, with all songs flowing perfectly into each other.
This album is just godlike, I feel like in terms of atmosphere and 'creating a feeling', this album is almost impossible to beat.
I might not hold it as my number one album ever, but I hold it very high, and it's just VERY special.
Untitled 7, the outro with Jonsi's haunting vocals = GOOSEBUMPS.
Those five would be good bets, even though I kinda had to leave out some other important albums.