I should get this out of the way right off the bat, I have not had very many good experiences with matcha. Matcha is a Japanese green tea that is very finely ground. Water is not poured through or steeped in this tea, instead the fine tea soaks in the water and is whisked to combine into a drink. So, you're not just getting the essence of the green tea, you're actually drinking the finely ground tea leaves as well. The tea is very bitter, very strong, and very popular with Japanese people. Matcha is the tea that is most often used in tea ceremonies in Japan, it's also a common flavour for cakes, sweets, and I've even had an icy made with matcha (that was a decidedly bad experience).
As I said before, I've had very few good experiences with matcha. The only exception might a green tea castela cake I had in Tokyo, which was yummy. While I can't say that these matcha Milkys are gross, I do think that the classic sweet milk flavour of Milkys covers up the gross matcha flavour. Instead the matcha flavour accentuates the sweet milky candy. In other words, if it weren’t for the sweet creamy flavour of the Milky, these would be terrible.
So, this is a case where a variation to a treat doesn't improve it, instead the treat improves the not so tasty variation. If you want to try something that is truly Japanese, then this might be worth a sample. It's not bad, but I would suggest that you buy a bag of regular Milky candies instead, and maybe follow it up with a nice slice of matcha castela cake.