overrated:
Cocaine (so yesterday.)
Vicodin, Percocet or Tylenol w/Codeine (please.)
Tramadol (people really like this dreck? plus it's an SSRI)
Soma (d00d i'm fu00rxed on teh muscle relaxerzz)
Ambien (d00d i'm fux00rex on non-bzdneodipine benzodiosp derivat ... oh never mind, lol)
Benzodiazepines (now that I think about it ...

)
LSA (slightly funny headspace and a bellyache. whee.)
Methadone (ugh.)
Buprenorphrine (double ugh.)
Underrated:
Alcohol (as a "serious drug", not as something that I indulge in or advocate ... 137 days & counting...)
DXM (yeah drinking cough syrup is tacky but it's a serious drug)
Mushrooms (as far as intensity vs. recreational "fun" time goes)
Nutmeg (really. it was actually interesting, not that i'd recommend it)
MDA (sold as MDMA, that's another story, but a lot of people underappreciate it)
Propylhexedrine (still sucks, but more rec value than you think)
Dexedrine (in my speedfreak days I preferred it to meth.)
Now I noticed a lot of people noted various psychedelics, esp LSD, as underrated. Well, in my crowd they're pretty highly rated

but if you don't, I suppose they belong there. Likewise most opiates. (I'm that all-too-common crossover 8))