Depends on your definition of good. Some would argue the elementalist is the weakest class while others would argue it simply requires the most skill to play effectively and for those who are both naturally very talented and willing to put in the effort to master a finger gymnastic intensive class, the elementalist can easily be as good as any other class. That said, I personally also feel a lot of the reason the elementalist is looked at so badly is because most players come in expecting the ele to be the typical mage, glass cannon, high dps low survivability, class. In a sort of bizarre twist, Eles are actually pretty sub par at dps out put, their AoE damage isn't bad (at least for now, anet is talking about nerfing AoE damage in the game) but their single target damage is extremely under whelming and nothing about their dps really stands out, AoE or other wise. Conversely, the class has made a name for itself at the higher levels due to extremely skilled players running what are known as "bunker eles", elementalists set up to control a specific area and more or less never die.
So in summation, as the ele currently stands, you generally want to pick an ele if you want to play the guild wars 2 equivalent of a tank, only with a lot more finger gymnastics and skill needed to actually do the tanking. If your looking for pure DPS, there's probably better class options to meet your needs.