Contra III comes back for revenge.
Graphically, Contra Advance looks pretty good. It's mostly identical to the Super Nintendo version, although bosses look much sharper and there's no slow down. The levels from Contra: Hard Corps don't look quite as nice, but it's not enough of a difference to effect gameplay in any way.
So yeah, Contra Advance is pretty, but the gameplay is where Contra Advance really starts to fall apart. First off, where are the bombs from Contra III? That handy weapon would clear the screen of any enemies, but for some reason Konami decided to leave it out. As if that wasn't enough, Konami also decided to limit you to one weapon. It was awesome to have two weapons in Contra III. You could blaze through the level with spreadshot or homing missiles while saving that powerful laser for the boss. But not in Contra Advance. And what happened to the levels in Contra III with overhead view? Well, they've been replaced with levels from Contra: Hard Corps. That's what annoys me most. I bought Contra Advance: The Alien Wars EX, I want to play The Alien Wars, damn it, not Contra: Hard Corps.
What happened to the music?! Contra III had an amazing soundtrack (the theme from level 3 is classic) and it fit perfectly with the mood: shoot everything. But Contra Advance changed the music for the worse. The songs follow the same rhythm, but they're high-pitched, annoying and just plain bad. Thankfully the sound effects have (mostly) remained the same, but you'll have a hard time hearing them over the horrible music.
Basically, Contra Advance is a waste of potential. Had Konami made it a straight port of Contra III, it would've been much better. If you're looking for a good shooter for the GBA, look elsewhere. Even if you're a hardcore Contra III fan, avoid this one and pop in the Super Nintendo classic.