It's a series that was made well before my time, and I actually only watched the first one last year. Now watched 2-4 as well, with 5 on my 'to watch' list.
I think it holds up really well, alongside your F13th, Nightmare and Halloween movies. I would argue that anyone who loves those classics of horror should really check out this overlooked series. I think after Hellraiser this would be my dream house that hasn't been done yet.