I hate to break it to you British guys, but Tracer sounds like a normal Brit. You all sound like that to us. *pats pats*
Heh, I've never really understood why some take umbrage to her voice. It's obviously exaggerated and goofy, but that fits with the OW vibe. Reinhardt and Junkrat are probably as far away from regular Germans/Aussies in terms of how OTT they are.
But, if you don't like the voice, fair enough. I find the Mockney accent more amusing than anything else, and I say that as a Brit. Your mileage may vary I suppose.
To answer why I like Tracer: She's bubbly and optimistic, but not hopelessly naive, and I just find her charming. Her interactions with characters like Winston are cute as well. I appreciate her outlook and personality - I feel it contrasts well with a lot of female characters in gaming.
On a more personal note, I also think she has the potential to be a great example of a LGBT character in games. I was ecstatic when Blizzard confirmed that she was gay - not because of some shipping shtick or whatever, but because she's a relatively normal and pleasant individual in her own right. I hope Blizzard reference it in-game soon.
Plus - she's a lot of fun to play. You can feel unstoppable when you get into a rhythm with her, and her playstyle consistently keeps things exciting.