The problem I have with Terminator 3 is that the story was ended so perfectly in Terminator 2. It would have been wonderful if they'd stopped there. If you look at the benefits modern technology can bring the franchise, all you have is improved special effects. Sadly, the actors who make the Terminator franchise what it is are either ageing or lacking in this film.
The way they just wrote out Sarah Connor for this film was very disappointing. Nick Stahl portrayed a completely unconvincing John Connor and his relationship with Claire Danes' character was just a completely cliched, hollywood coupling of two fairly attractive young people. There was no fire or real passion there at all.
Something you remember about The Treminator series is the resolute indestructable nature of the terminators. I don't think the Terminatrix took nearly enough damage to be considered a fearsome threat to Connor/humanity. I also think the way they finished her off lacked imagination too. I would have liked to see the ultrapowered electromagnet deliver the finishing blow. At least that would've been a bit more entertaining.
I'm not one who craves a happy ending, but the final scenes did leave a bitter taste in my mouth. And it was far too obvious that they'd line up another Terminator sequel. Here's hoping that they cancel it somehow before this excellent franchise goes the way of the Alien one.