Okay, I have to recommend The Wars series as one of my favourite turn based strategy games of all time.
This series has been going on for decades and I first got into it on the Gameboy Advance. The concept was novel to me at the time. Grid based warfare seems pretty simple, one might compare it to chess meets battleships but its executed so well.
The range of units, commanding super powers and fog of war make the mechanics of advance wars one of the most engaging turn based games I have played to date. If you're looking for something to kill time while going somewhere, Advance Wars is small but has just enough depth to keep you interested.
A true gem on the Gameboy Advance!
Yeah, I loved Black Hole Rising too :)