(See my thoughts on Pokemon Sapphire for most of my 3rd gen opinions)

In regards for Emerald, having the rival factions duel with each other to the point of worldly destruction was pretty cool. The Battle Frontier in this game was an awesome little tidbit in the game. Lastly, Rayquaza, the coolest looking Dragon type since Charizard/Dragonite becomes a vital part of the game and displays the mighty energy that it possesses. Also did I mention the trumpets in the soundtracks?