Well that's a good thing. Ignore the term thrash when applied to them. They are so much better than that. For your introduction may I suggest :
The Black Album (Metallica) - The best introduction by means of their most commercial album. It's in the top 20 selling albums of all time for a good reason.
Master of Puppets - Old school Metallica that's a little heavier but with a title track that is a metal classic.
Load - The album that took up a more bluesy guitar tone and they got their hair cut!
S&M1 - A brilliant collaboration with the San Francisco symphony orchestra that put a whole new spin on some of their classic tracks.
Avoid at all costs St Anger! The worst album ever by one of the world's biggest bands. An abomination borne of addiction recovery and navel gazing psycho babble therapy.
Disturbed - Sound of Silence
Great shout. First heard this version a few months ago at 04.30 in the morning, in a dodgy flat in Hastings whilst dealing with a suicidal mental health patient, playing it at full volume. Quite a surreal experience.
I can totally understand that whole situation you found yourself in. It’s such a black, dark interpretation that really hits home if life’s not going well, quite unlike the original.
It’s stunning.
(As an aside, hopefully the patient pulled through.)