No, Diet Coke doesn't taste the same as regular coke; but why would you want it to? As best I can tell, a preference for the flavor of sugared Coke over unsugared Coke is simply a learned preference like preferring Catsup over Brown Sauce or vice versa. I switched to Diet Coke many years ago, and these days regular Coke tastes wrong and not as refreshingly delicious to me. Stick with it for a while, and you not only get used to it. You come to prefer it.

In less sweet drinks like coffee, I'm not sure I could tell the difference between sugar and other sweeteners. FWIW, I do find that aspartame (Equal) works better in coffee than sucralose (Splenda).