This is sort of hard because as I'm thinking about each drug I'm trying to think of what the popular opinion is about it. I think also what some people need to remember is their first/best experience on the drug. I will often reference that here. Anyway, here we go. IMO:
Under-rated:
Opiates: Opiates fall into this category because I remember my first time with OxyContin, how I felt as though I couldn't move but how I certainly didn't care. And later, when I started to IV, that earth-shattering, orgasmic high from a good shot of dope or OC. Thus far in my experience in the drug world, this high is unmatched. Now, certainly not underrated are the associated risks. Once you have that feeling, all you want to do is get it back. However, used correctly, I think opiates are probably the 'best' drug.
LSD: I think part of the problem with LSD is too many people have this conception that they're going to see pink elephants and whatnot. This I feel creates the wrong impression. With good, clean acid you can have incredible fun, while also having a chance to get deeply introspective. It can help to show you the truth behind who you really love and who loves you, while also showing who you maybe don't like as much as you thought. Setting is crucial for LSD, but in the right setting LSD can be one of the best and most enlightening drugs there is.
Ecstasy(MDMA): Good quality MDMA can also be an amazing experience. Now, I was never into roll tricks, or raves, or glow sticks, or anything like that. Instead when I rolled I preferred to truly enjoy my friends. I just loved to talk the night away with good friends, about our dreams and our fears, the past, present and future, and it was beautiful. This was my favorite part about MDMA was everyone opening up to one another.
Over-rated:
Cocaine(even more so Crack): For me the high was always 'ok' I guess but very short and afterwards, even during the high, I was very anxious and sort of paranoid. Every time after it was over I thought to myself, "damn its over? thats it?" and I was pissed that I had wasted my money. Coke is a little different story, because if I do it right, I enjoy coke after I've been drinking. I should also say that the only way I do either these days is if I have an opiate to do with it, or maybe if I have a benzo to come down on.
Benzos: I seems like, where I'm from, everybody loves benzos. I've done xanax quite a bit, but even though I feel good, I don't know that I'd call it euphoria. Even if I did experience euphoria, I wouldn't remember it. I was hesitant to put benzo's in this category because I do enjoy them but I did so because of the negatives, at least for me. When I take Xanax, which is usually when I'm drinking, a few things happen, due to a total lack of inhibitions. I am a person of few inhibitions when I'm sober, so when benzo's and drinking get involved, watch out: I steal. I will steal anything from almost anyone. God forbid I go to a mall or something. Now, I'm usually like,"Man, I can't believe how risky that was." but I also am usually happy with my new merchandise. My morals in general get dicey. I also been known to spend all my money on whatever; drugs, food, etc. And I've also driven on a couple occasions when I should have kept myself in check. This once resulted in me wrecking my mom's car, terrible night. Lastly, I remember very little if anything when I do Xanax, which sort of spoils the fun when you don't remember having it. As far as Xanax without alcohol...nap time.
That's all I've got. Other drugs I wouldn't say are over-rated or under-rated. I think weed can be under-rated, but I won't list it here. I was also going to say the 2c family is over-rated, but I didn't do enough to have a valid opinion. Peace