The best thing Shudder have done that I've seen is the superb documentary Black Noire: The History of Black Horror. Absolutely essential viewing imo.
The other stuff they have made themselves I've not seen much of. I binged the first season of Creepshow and it was abit to hit and miss.
It's an acquired taste but I absolutely love Raw Force. It's low budget and bonkers zombie/cannibal/kung fu masterpiece.
Pontypool is superb and doesn't get mentioned enough.
Likewise to Prevenge.
There's actually tons of classics on there right now. Depends how much you have already seen and what you are after. There's a slew of Argento's Gialli that I would consider absolutely essential. American Werewolf in London, Phantasm, Intruder, Oldboy, It Follows, Scanners, The Raid, Hellraiser, Night of the Living Dead, Texas Chainsaw Massacre.
Then there is stuff that I love but probably aren't for everyone like Blood Rage, The Mutilator, Frankienstein's Army, Terrifier, Splinter, Behind the Mask: The Rise of Leslie Vernon, Your Vice is a Locked Room and Only I Have the Key, Class of Nukem High, Madman, Death Walks At Midnight, Death Walks on High Heels, Elvira: Mistress of the Dark, Toxic Avenger, Slumber Party Massacre, Demons, Don't go in the Woods Alone..., Evil Aliens, Thirst, House By the Cemetery,
Also Body Melt stars Harold off Neighbours.