Children of Mana is a good, but not great dungeon-crawler.
The Bad: even with dual-wielding and gem customization, the game has very little depth; enemies like to overwhelm you;
Children of Mana is a relatively shallow experience, no matter how hard it tries not to be. There are 4 playable characters, each one with unique stats. There are also 4 weapon types, of which you can equip 2 at a time. By equipping the right pair of weapons, you can set up combos and get out of tough situations. At any moment in the game, you can switch your weapon combination to solve puzzles or just add some variation. Unfortunately, no matter which weapons you have, the game is little more than alternating between the A and X buttons. "Puzzles" are little more than charging up the A or X buttons in the right places.
One unique aspect of CoM's battle system (really, the only unique part), is that enemies and certain environmental features bounce around when hit. Basically, this allows you to hit one enemy into another (which damages both monsters to some extent), or hit a barrel at a row of monsters. The same status effects that hurt you can also hurt enemies as well. If you knock monsters into a certain type of plant, they will become poisoned, and will take the same amount of damage as you normally would. Unfortunately, the rebounding effect is somewhat unpredictable, and applies to the player as well. Sometimes, the knock-back applied to you is completely exaggerated compared to what you can do to the monsters. Ultimately, this feature isn't really noticed after the first few dungeons.
Children of Mana tries to remain a similar experience to old-school hack 'n' slash games, so there are a few limitations that seem unnecessary. For example, you can save anywhere outside of dungeons (which is basically a single, small town), but when you're inside of said dungeons, you can only access the basic menu at checkpoints throughout the area. This can be annoying, since you'll level up quite often between checkpoints, but can't upgrade to higher weapons until you reach a midpoint.
Breakdown:
Presentation: There are a few extremely short animated sequences, but they feel unnecessary. And there's apparently some sort of plot, but nobody will be interested in it. 5/10
Graphics: It may be 2D, but it's nice 2D. Animations are a little basic, but overall, not bad. 7/10
Sound: Epic, and occasionally beautiful. Only a few are actually memorable, though. No VO at all. 8/10
Gameplay: Typical dungeon-crawling. Like pressing the A and X buttons repeatedly? Gems and dual-wielding add some variety, but not enough. 6/10
Lasting Value: The quest will take around 10 hours without side-quests. There are lots of side quests, but they all take place in previous dungeons, and add no variety. If you really like dungeon-crawling, the side-quests will last a few extra hours. There's also a multiplayer mode, but each member needs their own copy of the game. 7/10.
Verdict: If you're into dungeon-crawlers and desperately need a game that will last a decent length, Children of Mana is not a bad choice. There are better dungeon-crawlers out there, such as Summon Night: Twin Age.