I'd give some recommendations but I'd probably end up just repeating what others have said so I'll give some of my 'must haves'
:
Maudlin Of The Well - Bath / Leaving Your Body Map
These are actually two separate albums but they were released together and are meant to be listened together. What can I say about motW? Just pure musical artistery that every music fan should hear at least once! While the music is based around metal theres influences from post rock, jazz and classical with a unique and equally bizarre avant garde and doom metal overtone; the band is more like a small orchestra rather than you're typical metal band with multiple instruments playing at any time, most of which I probably can't even name! They even have three different vocalists for godsake! The music is of course weird, technical and experimental dealing with spiritual and occult subject matters that would probably fly straight over the average listeners head, but the underlying music is just downright beautiful and deserves a listen by any music fan let alone a metal fan.
Atrox - Contentum
A female fronted progressive/avant garde/symphonic metal band with probably the most bizarre, yet intoxicating singer I've ever heard. The music is equally bizarre with a very twisted, spaced out and almost schizophrenic atmosphere and did I mention the crazy vocalist?
Probably more of a marmite album but I definitely love it to bits.
The Gathering - Mandylion
This is how melodic female fronted metal should be done; utterley mesmerising with a gorgeously voiced singer.
Textures - Drawing Circles
Just downright awesome progressive tech metal/metalcore. The album has beautiful flow from start to finish with almost seamless transitions from head banging blast beats and chugging guitars to serene ambient landscapes. This is definitely one of those albums that is more than the sum of its parts.
Meshuggah - Destroy Erase Improve
Awesomely technical and almost mechanical progressive death metal. Polyrhythms, odd time signatures and robot like drumming is where its at!
Death - The Sound Of Perseverance
Top class death metal (well I'd call it 'classic' death metal) from the band that arguably started the subgenre in the first place.
Gorguts - Obscura
Definitely
the most insanely technical album ever to grace my precious ears!
Honestly these guys take experimental tech death metal to a whole new level that words alone simply cannot describe, its got to be heard. You really need to re-calibrate your preconceptions of musical composition to appreciate this album, though I admit its not for everyone since is brutal as brutal death metal gets and is well within the realm of artistic insanity.
Boris - Heavy Rocks
Not exactly metal, more like stoner/psychedelic rock with doom metal undertones. Whats special about this album is the guitar work, its like Hendrix but like x10 more deep, x100 sludgy, x1000 more filthy and equally fun to listen to!
Opeth - My Arms, Your Hearse
Opeth at their best in my opinion. Deep prog/melodic death metal that every metal fan should hear. I'm not a big fan of cookie monster vocals in general but Åkerfeldt's use of growling is spine tinglingly good on this album.
Novembre - Classica
Progressive doom metal from Italy. a lot like Opeth but less brutal and a lot more melodic imo. Sort of new to this type of metal myself but similiar bands are Katatonia (early Katatonia that is) and Agalloch both which are fantastic. Its doom metal so its inherently depressive, but its the sort of positive depressiveness that makes you feel good ... err does that make any sense?!
Eitherway, highly recommended.
Frantic Bleep - The Sense Of Apparatus
a lot like Tool and Meshuggah in terms of ambience and tone, but the album too has its own, unique awesomeness. Hard to put into words and theres very little that I can compare it too but if you like dark, cerebral progressive/avant garde metal, this is for you!
live they are **** 
