Nowadays, most acupuncture practices have evolved and adapted to suit modern tenderness - however, not necessarily advanced in benefit or efficacy. If the needles are as thin as hair, and also do not "stimulate Qi", then the needles might be just in the skin but not working on meridians. This is why modern acupuncture often does not attain substantial effect and is deemed 'complementary' to other practices.
In ancient time the metal industry was not as advanced, so our ancestors used gold and silver tools. As these metals are softer in nature, they were much thicker. And hence much more effective. In this regard, modern thin needles and the ancient ones don't compare. Also, some special techniques are simply impossible to perform with thinner needles. (Check out why)
Although most of the time I do not use needles as thick as the ancient ones, I work with needles slightly thicker than most of the acupuncture needles used today in practice. I needle free-hand which means no guide tubes are used to place the needles. This allows for a better connection, needle control and precision. You will feel that each needle activates Qi, and with it yields results. Like my master said, it is far beyond simply putting needles in certain points, but more importantly: the speed of the needles, the power in the needles, the technique that are used, and so on. That is why, while needling the same points, results can vary greatly between acupuncturists. It is actually very much like martial arts, it takes years of cultivation to put the power of the hand, as well as the power of mind, into the needles.
Overall, my acupuncture style might not be as pleasing as other styles, but it is very effective in treating serious illness - something I do with extreme care and utmost attention to your physical and emotional well-being.