In combat, the cleric isn't something that going to be a major encounter breaker. There's a few tricks they've got going for them, but having both played and DMed them, this isn't a class you need to worry about.
Outside of combat they can be a pain in the #@^ if the player decides to spam divination. Augury is primarily useful to let them know if they're going down the wrong path, but Divination and then Communion can be repeatedly used to try and get more information than the DM is ready to give out. I've found it's best to work with the player to have the spells provide the necessary information, but have their deity not appreciate constant "phone calls."
Oh, and be careful with Zone of Truth, which is can be a nightmare if you're not prepared. Make sure your mooks don't know everything, and the leaders be willing to die before giving up certain information. Otherwise, the players might simply hold someone captive until they fail the save, then tell them to answer or die, once again putting more information available than you're ready. Oh, and one loophole to the spell is that it's based on what the target believes, so they can "lie" if they think the lie is true.
Another important part of balance is concentration. Yes, the Spirit Guardians spell is powerful, but it requires concentration--which means that they cannot cast other good Cleric spells like Bless, Shield of Faith, Silence, Hold Person, Protection from Energy, etc. Certain magic items might also require concentration to use.
IME, Spirit Guardians ends due to a failed concentration save most combats. The cleric is going to be fairly close, almost certainly in melee range, and this spell draws aggro like crazy. My dwarf cleric took Resilient (Con) with an 18 Con to make sure this didn't happen very often, but even with Plate armor I still took the Dodge action quite a bit!