There is a lot to like about the 1995 Mortal Kombat movie. Christopher Lambert is charmingly impish as Raiden, God of Thunder, Cairy-Hirokyuki Tagawa is menacing as Shang Tsung, and the theme music is very memorable. The main cast of heroes is great too. They all have entertaining arcs that develop them as people while tying into the main story. All of them, that is, except for Sonya Blade.
Sonya's character arc starts off as strongly as Liu Kang's or Johnny Cage's. She wants to hunt down Kano, the man who killed her partner, and she sees him getting on a boat to the Mortal Kombat tournament. This gives her a clear motive for being there: revenge. It's very similar to Liu Kang's motivation: he wants revenge against the movie's villain, Shang Tsung for killing his brother. We see Sonya give chase to Kano, and we see the walls she has built up that keep her closed off from other people when she interacts with the other protagonists. Everything is in place for the character to receive as compelling an arc as anyone else in this movie, but unfortunately, it doesn't come together how it should.
The problem with Sonya's story comes when it's time for all of her set up to pay off; unlike the other main characters, her personal arc fails to tie into the main plot. Unlike them, Sonya's story starts to fall apart when she gets what she wants. Early on in the movie, the audience is told via a conversation between antagonists that Shang Tsung specifically wanted Sonya to take part, so he has teamed up with Kano. The mystery of why it was so important to him that Sonya of all people take part had the potential for some great storytelling.
Unfortunately, the answer to that mystery only serves to diminish the character. The reason her participation was so important to the villain's plan is that he was too afraid to fight the heroes in a fair match, and he figured that Sonya would be an easy opponent to beat. She's a skilled fighter and an experienced soldier, but the end of the movie throws all of that context away and just makes her out to be a lesser fighter for the sake of hyping Liu Kang up as the chosen one who has to save the day.
In fairness to the movie, it does attempt to show how Sonya has changed. At the end of the movie, she is kidnapped by Shang Tsung. He challenges her to fight because he knows if they fight he will win, and if she refuses then Earthrealm defaults, since he has taken her to a place where he thinks the other human characters can't go. Sonya refuses to fight him, choosing to believe that her friends will come, showing faith in other people. However, it still relies on her being "too weak" to beat the villain, and that faith she shows in her "friends" isn't backed up by the movie leading up to that point. They fight a bit together, but they spend a lot of it fighting separately, and Mortal Kombat fails to establish the bond which would lead to Sonya taking this leap of faith.
It could be argued that Sonya's treatment was just a side effect of having a game with an established "savior" who even a God is training to be the ultimate victor, but other characters show this isn't the case. Johnny Cage in this movie is a great example of how to develop a character who doesn't get the win, but still achieves plenty in his own right and grows on his own terms. He enters the tournament because movie critics and fans don't believe he actually does any of the fighting in his movies, despite the fact that he is actually a very skilled martial artist. He enters the tournament to prove them wrong, and gain some personal glory.
However, when he sees a character he befriended die, he realizes the stakes of the tournament, and when he steps up to fight tournament champion, Goro, he does so in order to fight for what is important. Later in the movie, Shang Tsung challenges him to a fight to decide the tournament, and Johnny refuses, recognizing that the fate of the world is more important than whether or not he gets the credit. Not only does he grow as a character, but the decisions he makes while growing affect the plot as a whole. In contrast, Sonya killing Kano is good for her, but doesn't do anything to thwart Shang Tsung's plans. If anything, her victory helps the villain.
Sonya Blade in the original Mortal Kombat movie had a lot going for her at first, but the movie didn't know what to do with her once she achieved her goal, and it all but shoved her to the side. She doesn't save the day like Liu Kang, and she doesn't score a big win for the good guys like Johnny. What development she does show doesn't feel earned, and only serves to show that the movie doesn't take her as seriously as the male protagonists. Hopefully the Mortal Kombat film due out this year will have a better idea of how to best utilize the character.