There are just so many factors to consider. First and foremost, how much you actually take. Not all pills are the same dose. And most of the ecstasy out there is already mixed with other chemicals, sometimes inert stuff like vitamins, sometimes more dangerous stuff like amphetamines or opiates.
But lets say you take pure MDMA (a common street name for this in the US is molly). Ecstasy mimics dopamine in the brain. This is a neurotransmitter that is responsible for a number of functions through out your body - these include heart rate, body temperature, appetite, mood and pleasure. The latter two being the main reason why people take it in the first place.
As far as what you might experience? Individual results vary. But most people report a sense of wellness beyond feeling elated. More like a state of complete euphoria. I suppose a "mental orgasm" is a fair metaphor. Some also report experiencing mild hallucinations and changes to perception of time or people's environment. People don't take it because it makes them feel bad.
That doesn't mean there are not potential negative side effects - it can increase your heart rate, few may experience panic or heighten anxiety (basically a "bad trip") it can increase your body temperature to dangerous levels - which is why people drink lots of water.
When it comes to MDMA compared to other drugs, its actually far less likely to kill you compared to other designer drugs such as other forms of amphetamines or opiates or even just too much alcohol. People who die or are injured because of ecstasy use, are so because they are involved in an accident (ie a car crash, or they fall and get hurt). The other reason is because they mix it with other drugs or the MDMA they take is not pure or is made incorrectly. As far as injury or death from MDMA itself, that is mostly caused by taking too high of a dose that causes the body to literally over heat and cook the brain. The other reason is that because people's perceptions can become so warped from the drug, the don't realize how much water they are taking in and die from water intoxication.
To me its not a question of whether or not people should use drugs in general. Its a personal choice and it carries positive and negative consequences. So does sky diving or bungee jumping. If you choose to use MDMA then you are also choosing to accept the consequences from your decision.