The Osutchi is the male version, and the Mesutchi is the female version. These were the first Tamagotchis with the ability to connect in order to mate.
There are two newly-added options, the last two select-able icons. One is for checking the TMP and one is for mating. This gives a total of ten icons, similar to the connection-era releases.
TMP stands for Tamagotchi Mating Power. There are four levels of TMP, and each level contains different obtainable characters. If two characters with the same TMP are mated, their children's level will be higher. If two of different levels are mated, the children will take on the lower-level. The current generation your Tamagotchi is on can also be checked here.
The second new icon added is for mating. When an adult character becomes old enough, they can mate with a toy of the opposite gender. There are two characters on each version that can't mate, however. The two characters obtained from neglect will always refuse to mate, as will the oldie-characters.
In order to use the mating feature, take off the tops, connect the Osutchi and Mesutchi, and press the mating icon in both units. If successful, you'll see an animation on both units, and two new babies will appear with the female. The male baby will soon go with the father, and the female baby will stay with the mother.
The two new babies won't be recognized as siblings, so you're free to mate them together once they're old enough.
The game in this one is pretty easy. Your Tamagotchi will hold a white flag on the left side and a black flag on the right. Press the left button when it's holding up the left flag, or the middle button when it's holding up the right flag. It's not hard at all to get a perfect game.
One thing that I've noticed about this one is that it's very musical. Mating, playing the game,hatching, everything seems to play a little tune. That's not bad though, since the sounds are pretty nice to listen to.
Every character has a counterpart of the opposite gender, which I find cute. As long as you don't end up with the neglect characters or wait too long to mate and get the oldies, it doesn't matter, though. Besides those, they can all mate.
They're both fun, but you won't get the most out of it without running both versions on your own or finding another person to play with you.