Fire Emblem on the Famicom is not a game that aged well in terms of graphics. But as a beacon of everything right and good about tactical/strategy role-playing games, it's still second to none. Forget Radiant Dawn on the Wii; the DS is where this series belongs.
Shadow Dragon is Marth's chapter of the Fire Emblem story, and Nintendo is relying on his Smash Bros. fanbase to overcome the 18 year gap between Famicom and DS. The game has got the full music/graphics makeover going for it, along with a pretty spiffy localisation job (somebody knows thy olde English). Alas, there's only so far cosmetic surgery can go; visually, Shadow Dragon just doesn't stack up to, say, Final Fantasy XII: Revenant Wings or Wild Arms XF. The talking heads cutscenes are pretty enough, but the Battle Chess-style fighting animations and map sprites look so pixilated you could grate cheese on them.
Forget the graphics, and focus on the gameplay. I slammed turn-based gameplay in my Fallout preview (and I'm not taking it back, so nya!), but I acknowledge it as a linchpin of SRPGs. It's also one of the biggest stumbling points for SRPGs on portable systems.
The goal of any "portable" game is that you can stop playing and put it down whenever you need to. And I'm not talking about just closing the DS; this might shock you, but there are times when you really have to turn the damn thing completely off. For SRGPs, this is a problem, because the good ones have battles that can drag out for well over half an hour. Shadow Dragon addresses this problem by adding a mid-map, one-use save point. This acts as a quicksave function, since you can usually bypass the save have one character close enough to it at any time to use it during a turn (before the nice flight attendant snatches the DS from you).
You can also use it as a halfway point to save yourself if you get owned spectacularly in the the last three moves of the battle. This is really handy, considering that Shadow Dragon practices perma-death. That's right. You can't revive your units at the next town. No matter how important they may seem to the story, they can die; and if they die, they're not coming back. Also, if they're carrying a quest item in their inventory (say, the Dragon Sword or a dungeon key), they take it with them when they die and you can really fuck yourself in a boss fight without that Dragon Sword.
Despite that casual slice of brutality, Shadow Dragon has a gentler side. You can scale back the difficulty from "merciless" to "hard" (yeah, the lowest difficulty setting is "hard" - they didn't screw around back in 1990) and go through the user-friendly tutorial that gently breaks perma-death to you about an hour in (even Marth was like, "He's coming back, right? Right...?!"). There are also "supplemental" chapters to the story, should you lose one too many story characters in battle. I had this super nice princess chick riding a Pegasus lead me towards her father's castle, only to bite it at the hands of a mage halfway there. Her daddy was awfully nice about it and two cutscenes later, I had a new Pegasus-riding chick from somewhere completely different that joined my party.
A major new addition to the game is the multiplayer mode. You can choose a unit you've trained and go head to head against a buddy on WiFi, or - if you're one of those "nice" types - you can loan one of your units to a buddy for them to use. I didn't get to see this in action, but I'm told that if you loan a unit, it's not like you lose it - it just creates a copy of it on your friend's game for them to use temporarily. A loaned unit will generate XP for the borrower only, I guess (lame), but if you're too lazy to train your own units in the arena, unit loaning sounds like a good deal.
A lot of care and attention went into bringing Fire Emblem: Shadow Dragon to the DS. It may not show in the graphics, but it's dead obvious from the moment you start playing, whether you played the original or not. The Marth factor might only matter to Smash Bros. fans (and there're four brand new prologue chapters for your back story fix); but SRPG fans owe it to themselves to give this game a go.