These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Award Snub: Not so much award snub as recognition snub; at the 2014 Grammy Awards Jeff Hanneman was not included in the "In Memoriam" montage that pays tribute to musicians who had died in the previous year. What makes it even more frustrating is that Jeff had been the recipient of two Grammy awards in the decade before his death. Naturally, this snub did not sit well with metal fans.
Awesome Music: Most of the band's output up to and including Seasons in the Abyss, at the very least. The music after that gets a bit more... controversial, although Divine Intervention and Undisputed Attitude at least are still generally regarded as worthwhile.
"Angel of Death" is definitely the icing on the cake. 5 minutes of pure, relentless Thrash Metal.
The fast, thrashing riffs of Reign in Blood or the slower, heavier songs of South of Heaven? Reign In Blood is either the band's best album or their Jumping the Shark moment depending on who you ask, with a Vocal Minority of the fans preferring the Epic Rocking style of Hell Awaits.
And then, there are those who feel the band jumped the shark when Paul Bostaph was hired as their drummer and, particularly, when 1998's Nu Metal influenced Diabolus In Musica was released. God Hates Us All is similarly polarizing, with many going as far as to say that the album was even worse than Diabolus (although it did give the band their first ever Grammy nomination with "Disciple"). Fortunately, 2006's Christ Illusion and 2009's World Painted Blood mostly rectified this by shedding the Nu Metal influences and returning to the band's thrash metal roots.
Dork Age: The Paul Bostaph period is seen as this by some. Diabolus In Musica, in particular, takes a lot of heat for its obvious nu-metal influence.
Harsher in Hindsight: Because of various issues, the release of God Hates Us All was delayed until September 11, 2001.
Magnum Opus: Generally considered to be Reign in Blood, although opinions vary and some consider it their Jumping the Shark moment. Hell Awaits and South of Heaven are also quite well regarded; there is a small but vocal minority that considers Hell Awaits to be the band's finest work.
Some fans consider Seasons In The Abyss to be Slayer's best album.
On a musical level, the Nu Metal-influenced Diabolus in Musica and God Hates Us All will never be forgiven by some fans. Even King isn't a fan of Diabolus.
Seasonal Rot: This has been levied at them. Fandom opinion is split about Divine Intervention, but Diabolus in Musica and God Hates Us All are near-universally despised; lastly, while most fans don't hate Christ Illusion and World Painted Blood, they also don't tend to be overly fond of them and view them as disappointing and unremarkable.
We're Still Relevant, Dammit: This trope was one of the main criticisms people had with God Hates Us All. The album contained quite a few Cluster F Bombs (which were, until then, a rarity in Slayer's music), similarly forced screaming in parts, and the same Nu Metal influence that permeated their prior album. Not to mention a pointless picture in the album booklet of a Bible with nails and the band name burned into it, which was clearly done for no reason other than to prove that they could still be "edgy" in the age of more extreme bands like Mayhem and Nile.