My issue with it is that all the units suck. Pretty well all of them have really bad growths.Shadow Dragon is ok too, unless you go into it expecting the same amount of character development and plot that the other games had. The other US-released FE games were very plot heavy. Shadow Dragon is not.
That was the main thing that annoyed me about Shadow Dragon. I got spoiled by all the other localized games where each character had about 3-6 supports and some kind of backstory. In Shadow Dragon it feels like the only difference between your characters and generic units are the stats and the face portraits. You'll suddenly encounter them, they'll be like "Oh hi, I'm joining you" and then they never speak again. Especially like when Ogma joins and brings 3 generic axefighters with him who exist only to be part of his little mercenary group.
Long story short: Shadow Dragon is fine as long as you're playing it solely for the gameplay and not the plot.
...Actually, I think the game got a bad reputation because FE1 was never released in America. Think about it; if we got the ancient NES Fire Emblem game it would probably be a beloved classic. Metroid and The Legend of Zelda have aged just as poorly as FE1 but look how they're revered. Remakes of really old games are usually well received because people realize it's a remake of an old game, and don't expect much. They look forward to the nostalgia. But since we never played the original (and no doubt a lot of casual players didn't even realize it was a remake of anything) the game didn't get that nostalgia bonus and was judged on its own merit. Basically an updated version of a 20 year old game was being compared to modern ones at face value. I think that's what the problem was.