I'm not always a fan of covers, because I like to hear artists be original and unique, but sometimes a band will take a song you love and make it even better often adding their own influence to the song to improve it. Here are some of my favorites:
Original: Slaughterlord - Legion
Even for someone like me who has listened to a lot of obscure metal demos with awful production this is a pretty primal track, both in terms of musicianship and production value.
Listen to how At The Gates - who set the industry standard for metal production standards in 1995 with Slaughter of the Soul updates the sound of the song and makes the song more accessible but still quite vicious. Legion was an awesome song before ATG covered it, but it wasn't played by awesome musicians or produced correctly. I suppose if you aren't versed in thrash or death metal it might still sound like noise to you, but to me the ATG version is crystal clear compared to the Slaughterlord version and gives the song the recording it always deserved.
Cover: At The Gates - Legion
Original: The Beatles - I Am The Walrus
One of the most popular songs ever. I love this song, it's a song you've felt like you've heard a thousand times before the first time you hear it. Maybe that's the Beatles being baked in our cultural DNA.
Boris and Merzbow take this song and drape it in their own artistic styles. The results is a delightfully desultory and dark version of I Am The Walrus. I don't listen to Merzbow by himself, but I think his talents are best realized in his collaborations, especially with Boris where his music can be complimentary and serve as a different layer of complexity. Boris' version is slower and deeper, less campy and more introspective sounding but with all the curious rhythm of the original. I love it. Listen to it loudly, if you don't listen to deep music loudly you aren't listening to it.
Cover: Boris with Merzbow - Walrus
Original: Grave - Into The Grave
Into to the Grave is a seminal track from the Swedish Death Metal scene in the early 90s. Generally when people think of the band Grave, this is the song that they are identified by. Grave never had the melody of Dismember or even Entombed, they were the more primal side of SWE death metal back in the day.
Funebrarum, old school experts making old school death metal with modern production and some modern influences, updated this song into what I think is its ultimate form. Unfortunately the version this user uploaded has some slight clipping which is a shame, but the chaotic array of the instruments in Funebrarum's production combined with the improved samples and musicianship make this an amazing cover.
Cover: Funebrarum - Into The Grave