Vala Mal Doran is a FANTASTIC character. She is one of the main reasons SG-1 kept such good momentum after its 8th season, and why Seasons 9 and 10 are probably my favourites of the whole show.
By the time the Ori are introduced, SG-1 is a well-known, well beloved cast of main characters of a well-established show. You've got the Dry and Witty Commander Jack, the Science Soldier Girl Sam, the Empathetic Nerd Daniel, and the Alien Warrior Teal'c. And this dynamic has kept the show going for 8 years.
But so much time with the same four characters doing the same things over and over is always going to get a bit stale eventually. Which is why when Richard Dean Anderson stepped back from the show, the writers brought in Ben Bowder's Cameron Mitchell to fill that void.
And Cam does a solid job. He's relateable and daring and he does the things Jack does with a bit of a different perspective, which feels almost fresh. With him, SG-1 is back to full strength, at least as far as numbers are concerned.
But that wasn't enough.
With Cam, the writers clearly tried so hard to signpost to the audience that he was worthy of taking up the Mantle of O'Niell, and with Zero subtlety. They literally had him pull a King Arthur's Sword from a Stone. He gets multiple focus episodes in Season 9 so he gets ample opportunity to flesh out his character and get some time in the spotlight to reinforce that he is a good fit for the team.
Then we get Claudia Black's Vala Mal Doran
She comes in as what could have easily been a one-shot character, immediately acting as a fantastic foil to Daniel, putting him off guard and proving that she is more than a match for him. In fact she proves herself so well that she ends up sticking around, because she's just so damn fun and charming next to a cast that is usually completely straight faced, without detracting from the immersion. So much so that she becomes a central part of the plot of the last two seasons.
I'd argue that she actually HELPS Cam's addition to SG-1 , because Bowder, try as he and the writers might, simply cannot substitute Richard Dean Anderson's fantastically dry humour.
Vala's flighty and unserious characterisation fill the void that O'Niell left in a way that Bowder simply didn't. Vala is witty and comedic in a way the show previously lacked, and on top of that capable and intelligent without overlapping Sam or Daniel's character niches at all. She gets on Daniel's usually unflappable nerves, which give his own character great opportunity to shine in it's own right in new ways. And most improtantly, she is also the most HUMAN member of the team, despite ostensibly being an "Alien". She is flawed, she is selfish, and she often acts in the interest of personal gain, which are traits that were not previously present in any of the original members of SG-1, nor Cameron Mitchell.
I think Vala actually ends up being a much better character than Cam because while the former needs a lot of help from the writers to fill an exisiting niche, Vala creates her own. She's not military, but she is still extremely capable, as shown in her very first episode when she takes over the Prometheus single-handedly. She's doesn't immediately embody the values that SG-1 is known for, but she is shown time and again to have a good heart and that when push comes to shove (and sometimes a push is necessary) she will choose to do the right thing. While she, like every member of the main cast, falls occasional victim to the writers, Claudia's performance consistently shines, and brings a lot of life to what had become a very procedural and predicable cast and narrative. Not to say the show doesn't remain relatively predictable, but Vala's character adds a new aspect to the interpersonal dynamic of the main cast that keeps the usual beats feeling fresh.
Her personality and character add a lot of depth to SG-1 and enhances the characterisation of Daniel, because she's giving him a character to respond to and play off in ways he hasn't had an opportunity to before, rather than just what he usually gets, which is text to translate or ethics to whine about. Vala being Vala not only adds a whole new dynamic to the main cast, but it gives Michael Shanks the character focus he was so desperate for when he briefly "left" the show.
It may be a controversial opinion, but Vala Mal Doran is a BRILLIANT character AND addition to SG-1 and the team did not come into its own after O'Niell's departure until she became a main character of the show.
