Best as a novelty
I mainly bought this for my collection, because I have fond memories of these games, and because I like the oddly colored cover art. I already have the US versions of each, and they seem to be exactly the same here as their individual releases.
MK1 is a terrible port. Johnny Cage was removed, the controls have a significant delay, there's tons of censorship, and the Fatalities are ridiculous. On the plus side, it was the only version of the original MK where you could play as Goro.
MK2 on the other hand, is much better. It still had to be cut down, less characters, less finishing moves, no blood, but it still came out really well for the hardware it's on. It's the best MK game on the original GameBoy by far, and it was the best portable MK for a long time.