Lunar: Dragon Song's extensive flaws far outweigh its charm.
Those familiar w/ the Lunar games will find the story here very familiar. In fact, it is identical in many aspects to the story of both the original game in the series, its remakes, sequels and remakes of its sequels. Those who do not mind a rehash will find some appeal here but the only real twist is the same twist as in other Lunar games only poorly paced and plotted in this case. If you don't mind a very standard boy-meets-girl, boy-fights-evil type tale, I guess it is passable as skeleton to justify the gameplay.
Unfortunately, the gameplay is where this really fails. Lunar: Dragon Songs battle system is a few steps backward from the original games in the series. While its predecessors feature a strategy-based battle system, where your party can move and select multiple enemies to attack, here you are pretty much just given the option to attack or use a magic spell and even which enemy you target is picked either at random or by some very, very poor AI. You have to go a long way back in the history of RPGs to find a battle system w/ this little control. It's truly awful.
To make matters worse, you don't even get to gain experience and items in the same battle. You have to pick between the two. And still worse is when you are collecting items, most of what you get isn't even useful on it's own and you have to do special little sidequests to earn money which you can then use to buy useful items. While many will be happy to know that Lunar: Dragon Song does not have random encounters, this is completely mitigated by the fact that your only real way of earning money relies on random drops from enemies. While I could see a system like this working if it was thoughtfully designed and tested, it's half-baked here and it proves only to artificially and annoying extend gameplay.
Despite all this, battles are by and large quite easy. Early in the game, enemy parties can be defeated simply by attacking over and over and later, you simply cast a few spells to soften them up and then attack over and over. The game's designers seem to realize this and include an AI function and a button to speed up so you can just get the battle started and go ahead and read a book or something while it plays out. This hold true up through and including the final boss. There is really not much challenge here.
So that is Lunar: Dragon Song: It has a decent if series-standard story, poorly executed w/ poor gameplay and not enough content or challenge to fill out the approximately twenty hours or so it takes to get though it. This is perhaps worth playing if you just can't stand not knowing about this small segment of the Lunar universe or have already played every single other RPG on the DS. Otherwise I recommend you not waste your time.