Jesus.
Shaman buffs are so easily covered by the rest of a raid. In 25 mans, the only totems that bring any sort of buff that shouldn't easily be covered by other members are Totem of Wrath (Replaced with a Demo Warlock if you have one, which most raids now should because of +400 sp to the raid), and Wrath of Air. Whoop-de-do.
But anyway. Shamans are not OP. You can't raid heal AND tank heal in the same fight, because doing so requires completely different itemization (Haste vs. Int). If you take a resto shaman and a resto druid, same gear level and same skill, and ask them to raid heal, the resto druid will offer more. Chain Heals have this nasty side-effect of not being able to reach ranged which are far away from each other (Which is actually a good thing for half the fights in end-game right now where you need to be 10-12 yards away from everyone for whatever reason.
If you pit a tank-heal geared Shaman against a paladin for tank healing, even if the paladin is terribly geared the paladin will probably be better. If you want to talk about an OP healing class right now, making Beacon of Light duplicate overhealing as well as effective healing made them almost essential to any raid now.
I'm not bagging on resto shamans. The fact that their biggest aoe heal is a smart heal is amazing for the most part. However, if you're winning in meters on almost every fight, that says pretty negatively on your guild.