If you've already played extensively with the various vanilla farm maps, or even if you haven't, it might be fun to try a custom farm map. There are lots of good choices; I'm fond of
DaisyNiko's maps myself. If you go with one of the larger-than-vanilla maps, Golden's suggestion of Tractor Mod is even more important.
If you want a significant visual departure from vanilla, you could also use a recolor mod such as
Starblue Valley or
Eemie's Recolor.
If you want to expand the farming experience itself, take a look at
various PPJA mods. They add enough new crops, recipes, machines, etc., to let you try all kinds of farming.