This season is one of my favourites because I think it was when Charmed really started to pick up the pace a bit. Obviously I enjoyed seasons one & two otherwise I wouldn't have kept watching but season three will just blow you away from start to finish.
It begins with Piper and Leo trying to adjust to life as a couple when they are forbidden to be together. It also introduces a new character, the rather gorgeous Julian McMahon who plays Cole. He was sent to destroy the Charmed ones but instead falls for one of them-the beautiful, fun Phoebe. So this season concentrates on romance for two of the sisters, Prue however doesn't really have any romantic action this season. She goes on a few dates but her heart doesn't really seem to be in it. I don't think I would have liked to see her with anyone else as I thought she and Andy were really sweet together, plus it would have been a bit pointless to set up a new romance for her as this is her last ever season in Charmed.
Standout episodes this season are: The Honeymoons Over(great season opener, indicates where this season is going), Power Outage (to see Cole struggling with his dark side), Sleuthing With the Enemy (Phoebe discovers Cole's true nature), Coyote Piper (fun, also one for male fans as Holly Marie Combs wears a sexy outfit and does a dance that has to be seen to be believed), Bride and Gloom (the sisters turn evil and its fun to see what they're like), The Good, the Bad and the Cursed (it's unusual and takes a new twist on the traditional Western), Just Harried (Piper's wedding day=disaster), Sin Francisco (it's hilarious, especially Phoebe) and All Hell Breaks Loose (probably the best but most tragic episode out of all eight seasons).
The other episodes are good in parts or just okay. Some have really good ideas like `We all scream for Ice Cream' but just didn't really grab or convince me as much as the others.
This season Prue is the most powerful. Phoebe does gain a new power to levitate, which is good since she's always had the least active power of premonition. Piper gains a new power in `Look Who's Barking' which she can't control at first cue clocks flying off walls and watermelons on ceilings; it the power to blow things up. Prue got her power to astral project last year which she puts to some use this year. She doesn't gain any new powers this year but she is suddenly a kick-ass fighter. Although she did say she was going to a kickboxing class last year with Phoebe in `Ms Hellfire' Prue is a better fighter than Phoebe by the looks of things (watch `Wrestling with Demons' and you'll see what I mean). I have been doing kickboxing myself for five years and I know there's no way someone could be that good a fighter after just a year of kickboxing classes, so Prue's brilliant fighting does not make sense. However I didn't mind too much as it was cool to see her kick some ass, plus the Charmed ones are definitely more powerful now than they had ever been the two previous years.
Finally this season also sees the departure of Prue. Shannon Doherty's reasons for leaving all seem to be hearsay but one rumour was that she didn't get along with Alyssa Milano (they are hardly in any scenes together in the last six episodes or so of this season, coincidence?) The last ever episode with Prue ends on a cliff-hanger. Both Prue and Piper appear to die and Phoebe is trapped in hell, so the fate of the sisters seems undecided (this is never properly explained-see start of Season 4). The episode is extremely heart-breaking with Shannon Doherty giving her best performance ever, lashing out against the reporters outside her house & the police in the hospital, and then her tear-jerking reaction to Piper saying `I love you' and then (temporarily) dying from a gun-shot wound. By the way this episode definitely deserves the 15 certificate it is given as Piper getting shot is quite bloody.
Anyway this season is one of the best so I would definitely recommend adding it to your collection.