With any
drug, a first-time user may discover that they either do or do not enjoy the drug's effects. Some drugs, such as
DXM or
DMT, are not appealing to the majority of users.
MDMA, however, has one of the highest "approval" rates of all
recreational drugs. Assuming one obtains a
pure pill, it is pretty difficult for someone to have a bad time while under its influence.
That being said, there is plenty of hard evidence out there that frequent MDMA use IS harmful. While studies based on infrequent users are currently inconclusive (although so far signs suggest it's probably fine), those who take MDMA at recreational doses more than once every two weeks have been definitively shown to take on some amount of brain damage, affecting the overall cognitive ability of those individuals. Although it is not yet clear whether this damage is permanent or temporary, it has been shown to last at least a year or two.
A more immediate risk of MDMA is dehydration. Many users become energetic while rolling, and will more likely than not want to run around or dance (yup, this means all you ravers out there.) It is not uncommon to push your body's endurance a ways beyond what you would otherwise take on. Dehydration is probably the most severe risk for users of pure MDMA, so remember to take some breaks and cool off once in a while, as well as drinking water frequently.
Note that consumption of alcohol while on MDMA is a VERY bad idea; it complicates your bodily processes in all sorts of nasty ways, the most obvious of which is that alcohol is in itself a dehydrant. It should also be mentioned that anyone regularly taking anti-depressants/MAOIs should steer clear of MDMA; not only will they not feel the effects, they will be taking a very serious health risk. (There was even an episode of Dawson's Creek that dealt with this.)
Finally, any prospective user should be familiar with all of the drug's effects, and be prepared to accept any consequences of their actions while under the influence. In other words, unless you're confident in your ability to control yourself in this altered state of mind, don't be surprised to wake up next to your idiotic ex-boyfriend and totally regret telling him the night before that you loved him all along, which for some inexplicable reason seemed like a good idea at the time.