The best Gen III experience out there. RSE but harder, adds more mons you can use, better distribution of new mons, the only issue is Wallace being a lamer Champ than Steven but it makes a little more sense balance-wise. Oh and the story being kinda weird with no major fight you just have Rayquaza come in shoo the legendaries away and the end no major fight.

Still, if you wanna play GBA, play Emerald.