The Druid of the Land is severely lacking in both power and flavour. I think a very simple fix that can help this while still not being overpowered, would be to allow a Land Druid to add a new circle at 5th, 7th, 9th & 12th levels. The circles only add to prepared spells but give them greater spellcasting flexibility, which is what the sub-class is meant to be about. It also helps with flavour because instead of being merely an "Arctic" druid, you increase your influence over the various circles and finally become a name-level druid at 12th-level after mastering five circles.