At first, I didn't expect to have much interest in Sayaka. There were some intriguing hints that she was up to something, but I still slightly resented the game for making us spend so much time with her when there were other characters I was more keen to get to know.
And then she tried to frame us for murder, which is objectively a pretty interesting thing to do!
I love the questions Sayaka leaves behind. In the end, did she care about Makoto at all? Did she feel bad about her plan to frame him; did she feel bad about killing Leon? Would she still have been so friendly with Makoto if she hadn't been planning a murder?
All those answers died with her. All Makoto can do is miss her, with no way to know how much of their friendship was real.
I'd love a glimpse of the alternate universe in which Sayaka succeeded in her murder plan; how would she behave during and after the trial? But, alas, we'll never see it. I... I assume. Now that Danganronpa 2x2 has been announced, I suppose anything is possible.