I don't mind them. I find there are better ways to do battles, but random ones on an overworld is fine.

However, when the encounter rate is not just right, it can be the most frustrating thing. Too high? Ugh can't move a step without getting into a battle. Too low? That boss you're struggling to beat? Good luck leveling up to beat him. A nice balance (or like in Bravely Default with the adjustable scale).