Pink Floyd is the Pink Floyd of Classic Rock.
There is a reason that any modern band with progressive, space rock elements is referred to as the "Pink Floyd" of its respective genre. Pink Floyd is a very important figure in rock history, and anyone who claims to be a fan of music should hear this album at least once.

Fantastic music
I have always loved this album... I was sitting in a coffee shop with one headphone in and one out. And the part on 'the dark side of the moon' when the luner laughs, LOL, I actually turned around to see if someone had laughed behind me... It was hilarious, I giggle about that every time I hear that song...

Overrated but still awesome
I think Meddle is a better album, but this is the album that everyone will remember Pink Floyd by. And it's better than most bands will ever put out so it's hard to fault it. Anyone who likes rock probably ought to add this to their collection. There is a reason why this is one of the top selling albums of ALL TIME. It is a monument of rock - almost anything Floyd was ever involved with was.

I find it boring
This record is so boring, like most of Pink Floyd's work. All the songs are very s-l-o-w, they make me wanna sleep. Look at the reviews below: everyone seems to be trying to write a novel or a thesis about it. By the second paragraph i'm already yawning. Can't people be objective? I guess too much Pink Floyd gets you that way.

Is This The Best Album Ever? Probably.
And here's why. Before this album, Pink Floyd had somewhat of an interesting catalog. With Piper, Syd created some seriously whacked-out acid rock that's cool and all, but really hard to get into. They showed they were capable of writing some cool stuff, in a little bit of Saucerful of Secrets and Ummagumma and stuff, and yet, on these same albums, there was weird excessive experimental stuff that was just hard to listen to. Then they put out Meddle, and that was their first fantastic album. But it wasn't exactly cohesive. They churned out ballads (Pillow Of Winds), space-rock jams (One Of These Days), streamlined prog (Fearless), blues (Seamus), tropical grooves (San Tropez), and epics (Echoes). All these were great, but they didn't connect. Then, they made Dark Side.

They took all the great elements from pretty much every single one of their albums: be that sound effects, fantastic harmonies, electronica, killer guitar solos, smooth vocals, outstanding cynical lyrics, or trippy chord progressions, and fused it into a single album. I prefer to look at DSOTM as a single song; there's not a song on here that I really like to listen to out of the context of the album, with the exception of maybe Money. But that's because the whole album works. The whole album fits together like a machine and welcomes you into it (get it? Haha, Pink Floyd humor) from the very first heartbeat. It's a beautiful album, and not much more needs to be said.

But then the other reason that this is Pink Floyd's greatest is that everything afterwards wasn't quite as good. Wish You Were Here is a fantastic album, but the concept just isn't as unifying as DSOTM. Animals was alright, but it had some pitfalls, and this was because one: they were trying to make another DSOTM that had all these qualities, but with weaker material; and two: Roger Waters was beginning to morph into the egomaniacal tyrant that he became on the Wall (just too weird for me, sorry Pink Floyd purists) and then The Final Cut, which isn't even a true Pink Floyd album. A Momentary Lapse of Reason and The Division Bell are certainly underrated, but I think that although Waters was a tyrant, his absence from those albums prevents them from being the masterpiece this album is and always will be.