My experience with Moon 12 (medium) was also a disappointment. Maybe it was the rubbers I compared it to, but it felt like several leagues below the competitors (Hammond Z2, Omega 5 tour, and H3N Nat Bs 40) during a 3-4 hour session. I think the rubber is made solely for the backhand, because it just plays bad on the forehand.
I will try to break it down a bit:
1) grip - good, the rubber feels semi-tacky and grips the ball well.
2) blocking - good but not excellent. I expected the block to be a bit better, especially after I applied 2 thick layers of booster. Without a booster the rebound was so low I was scared I wasn't going to send the ball over the net. So it's pretty easy to block the balls, the rubber kills the incoming spin and returns slow awkward half-long balls. However, an experienced opponent can keep going with attacks as such blocks don't pose any threat.
3) flat hitting - average. Although it's pretty easy to hit the ball, the speed has its limits, which aren't high.
4) topspin/spin - just BAD. It's easy to spin the ball to a certain degree, but the amount of that is spin low. At no point was I or my partner able to spin the ball where it would be dangerous.
5) serve/receive - below average. The rubber produces little spin on serves. While it's good at ignoring the incoming spin during receiving, you also don't produce much of your own.
The rubber felt much deader than I expected. For me, it only became playable after a booster, and even then it was much slower than soft European hybrids.
The feel was very similar to softer versions of Jupiter 2 but way less tacky.
I think it's a decent rubber for beginners and I even wish I started my TT journey with this rubber instead of Venus/Mars/Mercury/Jupiter. It's all about control but it also doesn't cause trouble for opponents.