I've been playing the entire Millennium series several times since the first part was released and loved it from the start.
There's this young girl, determined to change her fate against all odds, and the story is well told, so that you feel with her the injustice that happens to her and her family.
The main quest of the game is to find people who are willing to fight alongside Marine and I've always been curious about what the next character will be like, what abilites they are going to have. Their strenghts and skills are very diverse and it's fun finding out how to use them best and what they can do.
Also in their personalities the characters are very different, which is typical for Aldorlea games. Each one of them is special and I loved reading the dialogues between them.
The gameplay is very well balanced. You can choose the difficulty mode that suits you best, and an "ordinary" player like me can do perfectly on normal mode. Fighting in that mode isn't too easy so that one would get bored, but also not annoyingly hard, and grinding isn't necessary at all, which is something that I appreciate.
Being granted the choice whether to play with visible or invisible encounters is a great feature too and increases the replay value a lot in my opinion.
What's typical for Aldorlea games as well is the big variety of equipment. You often find great stuff in secret rooms, but also get to buy good things. It's so much fun to find new weapons and enjoy seeing the difference they make in fights, as well as other special accessories.
A big (albeit totally optional) part of the game is finding secret rooms. I love and hate them. It's always satisfying to find one, but it can become just as frustrating when missing one or more.
There are also a lot of side quests to do, some easy, some quite tricky. So this is a game where you shouldn't just rush trhough, but take your time and explore thoroughly. Then it's fun to figure out how to solve those quests.
As for visuals, I find the maps very appealing and beautiful. What's special in MM is that there are maps where you can only walk left and right and jump up and down to other platforms. I like that, it's different from common maps. Also you do a lot of crazy jumps to reach places, that's awesome.
The character artworks are probably the most beautiful of all Aldorlea games, they are simply amazing.
The music too is wonderful for the most part, at least to my taste.
All in all I very much recommend this game to all people who love old school RPGs and are not biased against RPG Maker games.