NyQuil is one of those things that you wish didn't work so well. The reason I say that is because of its AWFUL taste! It's thick and syrupy, which is not really the problem. The taste is pretty indescribable (not in a good way). Ironically, when I first get sick and take my first dose, which happens to be quite a large one, the taste is tolerable. However, when it comes time for the second and third doses, it makes me gag. The recommended dose for an adult is so big that I can't swallow it all in one gulp; it usually takes about two. Yet it works so well that I force it! "Why not take the capsules instead?", you ask. I am one of those people who cannot swallow pills bigger than the size of a pencil eraser. Plus I tend to have more faith in the syrup versions of medications.
It knocks you out, which is a good thing because once I wake up, I'm usually feeling a bit better and less lethargic. Do not take it if you have important things to do. NyQuil will generally have you feeling better in about 2 to 3 days, depending on how severe your cold or flu is. For me, it helped every symptom it listed, which has been the only cold/flu medicine to do that.
I highly recommend NyQuil, especially this flu season. If you're extremely picky about the overall nasty taste of medicine, I must warn you that it will be difficult to swallow; but it is worth it. If you won't have a problem with the taste, then chug away and feel better!