I believe you are confusing three different things, hearing threshold, equal loudness and head related transfer functions (HRTF).
Hearing threshold refers to SPL where certain sound is audible. This varies between frequencies. Human hearing is more sensitive at mid frequencies, and less sensitive at higher and lower frequencies (humans are optimized to hear speech frequencies). Check Armaegis' link on equal loudness. At the bottom there is a figure, and the curve, labeled threshold, shows an average hearing threshold SPL for humans.
Equal loudness contour (curve) tells the SPL needed for different frequencies to sound equally loud. Let's take the above mentioned hearing threshold contour as an example, a 100 Hz sinusoidal should be played 25 dB louder than a 1 kHz sinusoid, in order to make them sound equally loud (or audible, in this case, as we are using the hearing threshold levels). This phenomenon varies also as a function of SPL, you need to pick the curve (or contour) that matches your listening levels. The louder you listen, the differences get smaller. If you have sometimes wondered why bass "kicks in" once you have turned the volume up, the reason is that as you increase the volume, hearing sensitivity increases more rapidly at low frequencies than in mid frequencies.
Head Related Transfer Function (HRTF) refers to sound transmission from a point in the user environment to the user's ear canal/drum. Let's say you have a loudspeaker in front of you and you have a miniature microphone inside your ear canal. Now making a frequency response measure will give one HRTF measurement. The result will be different for each human. If you want to design a headphone that sounds the same as listening to a loudspeaker, then the headphone should produce the same frequency response at the microphone as the loudspeaker. As the result varies this brings up one big challenge in headphone design, how to make a headphone that sounds good to as many as possible. Some headphones just work for some, while totally failing for others.
So, if you find a reviewer who likes the same headphones than you do then perhaps you can trust his/her opinions a bit, and vice versa, of course.