Terraria is a bit of a sandbox RPG fusion, as far as new games go it's pretty cheap too
For GBA try Final Fantasy Tactics Advanced, that game kept me interested for quite a while.
For DS there's an odd game called Contact, I found it a bit of a curiosity. As far as RPGs go it's not amazing or anything (actions a bit boring), but something about the presentation really surprised me - it wasn't your generic everything always ends well type of RPG, sort of like an actual person much of the game you don't actually find out what was the fruit of your labor or even why you're fighting in the first place, it also brings other interesting factors into play such as the idea that you as the player are manipulating the lives of those in the game and is your interaction really for the better?
I wouldn't recommend buying the game but if you could emulate it and you're bored it's at least worth a try, as I said I found it more a mental curiosity then anything else.
