You may not be able to tell the difference between Splenda and Sugar but I could. I soft drink brand that I like started to add Splenda to their products. I forgot about it until my wife gave me one. After drinking a few mouthfulls, the taste reminded me that they added Splenda because it really didn't taste the same, even with some sugar in the mix. I looked at the label and my suspicions were confirmed.
It's a lot closer to sugar than any other artificial sweetener that I've tasted but not quite the same. Of course I can also tell the difference between sugar and corn sweetener.
The difference that occurs to me is that of texture. Splenda is, of its very nature lighter in texture.
I find Splenda to be a very useful product. But then, some of us are very sensitive and should, perhaps, not explore new products in this very imperfect world in which we live.