You don't have to tile all the grass. You could just put a plain green background, with grass tiles in patches.
It might help to put borders around these patches too, combine that with roads and other objects, it won't look so bland and tiled.
But there may not be anything wrong the tile itself per say, you just can't overuse it like that. Look at Legend of Zelda III, Final Fantasy 6, and Seiken Densestsu for more inspiration.