Today I tried my first Diet Coke Sweetened with Splenda, and must admit general disappointment. It's too treacly for my taste. I generally favor the bracing taste of Diet Coke over Diet Pepsi's sweet aftertaste. I really like the Diet Cokes flavored with vanilla and lime. (A former coworker told me his family even preferred the taste of Diet Vanilla Coke over sweetened Vanilla Coke.) But this just tastes like watered down corn syrup.
I'm really surprized. There are several Waist Watcher sodas that my wife and I enjoy, particularly the Diet Black Cherry. They're all sweetened with sucralose. I use granular Splenda on my breakfast cereal; my wife uses it in her coffee. I'm not sure what Coke has done to their flavor other than substitute Splenda for aspartame, but it's not good.
All in all, I sincerely hope the new formulation will be only an alternative, and not a replacement.