I'd second Terranigma, a great game. Actraiser was also pretty fun.
Other SNES games I would recommend... Lufia 2 (or just known as Lufia in Europe since the first never came out here) was a great game. I know you dislike the DS remake, but this is completely different and far better, in my opinion. The original Lufia that was never released here is also a good game.
If you have another person to play with or like action RPGs, then Secret of Mana would also be a good choice. It plays similarly to Ys 5, but the gameplay is better overall (and it still has some nice music, like the Ys series).
Oh, and if the flashcart permits translation patches, you should get Der Langrisser. An underrated SRPG in the vein of Fire Emblem, but arguably more challenging. The creators also made the Growlanswer series and the Devil Survivor 1&2 later, but I still prefer Der Langrisser over them both. It also has four different story paths.