There's nothing original about Charmed at all. It's actually more of a rip-off of Joss Whedon's stuff than the movie Practical Magic.
I watch it, occasionally, but only for the boobies and hot chicks.
Let's see, it's about 3 witches which isn't exactly original.
Buffy the Vampire Slayer starts to get really popular, so what does Charmed do? They add kung fu to it by giving Phoebe (Alyssa Milano) kung fu skills.
BTVS had an incredibly engaging storyline of the heroine, sworn to kill vampires, falling in love with a vampire (demon). Charmed then did the same with the Phoebe (witch) and Cole (demon...which witches are sworn to kill) story line.
BTVS's Buffy and Angel storyline also had Angel go bad (he actually is bad, as he has a good, human side, and an evil, demon side) when Angel turns evil and tries to kill everyone. Buffy eventually has to kill Angel (but he comes back). About a year or two later, Charmed has a storyline where Cole (human good side, demon bad side) turns fully evil and Phoebe and the gang are forced to kill him (but he comes back...and is eventually killed "for good" later...when he leaves to star in "Nip/Tuck" on F/X).
I could keep going on about how many other story ideas they stole from both BTVS and the Angel series, but it'd take all night.
Bottom line, Charmed is one of the worst shows on TV, writing-wise and originality-wise. However, it is decent eye-candy.