I just finished this game up a few days ago, and man was it incredible. I put about 50 hours into the game before beating it, making it my longest, single playthrough on a portable RPG ever. I could have beaten the game a lot sooner than I did, but I wanted to do all of the sidequests and do a good bit of leveling and AP grinding.
The port is really good, and the only thing that really suffers on the downscaling to the GBA is the music, but even the music is impressive for a GBA game. There is a new translation which may irk the fans of the SNES game, but I found the translation to be decent once you get used to it.
Overall it's a great game and quite possibly one my favorite games of all time. A heck of a lot better than the crappy Final Fantasy IV Advance port.