F.U.B.A.R.
Bluelight Crew
MDMA can be extremely hit and miss. Especially once you're accustomed to / bored of the effects.
Of course, you could put it all down to certain batches 'lacking empathy' and formulate wacky theories about synth routes. :D
Same with all drugs really.. Having said that, you just 'KNOW' when you get a really good batch of something - IME, if you have to question its effectiveness, then it is undoubtedly shite!