The essential element, the sine qua non, of a good tamal, but especially a tamal de rajas, is good masa. With a tamal de rajas, you have nowhere to hide, no mole sauce or meat to take up the slack or disguise brittle-textured, lumpen, or flavorless dough. There is nothing but cheese, chile and dough between you and nirvana.
Of course, it's better to make your own, and the oft-hidden truth is that it's really quite simple. If you want to know the secret, you have only to write to us, and we might risk life and life and disownment in order to give it to you.