Advance Guardian Heroes is only going to appeal to longtime fans of the Saturn original.
The reason for this? The game's slow, unforgiving, and poorly implemented on the GBA hardware. You will plod your way through levels, doing your best to block with the shoulder buttons and nail all the precise jumps required of you, but more often than not, all but the most steadfast players will fail. It's not so much that I have anything against the game for being hard, but a side scroller's controls should never be this difficult to pick up and start playing with.
Everything about Heroes is clunky and obtrusive; the polar opposite of what is usually associated with the Treasure name. You can give your character upgrades in RPG style stat screens between missions, but most players won't last that long. The game starts out slow, the difficulty starts high, and the majority of folks who pick this up will find it nearly impossible on all but the lowest setting. That said, if you can wing the hard difficulty, you're looking at a mere couple of hours before you see the credits.
Visually, the game fares pretty well for a GBA game, but the sound and (written) dialogue are both pretty much horrible. Any which way you look at it, Advance Guardian Heroes is another case of a classic game getting a not-so-classic update.
-George