Holy Power was a really good idea, but implemented really poorly during Cata, where Crusader Strike was the only way to generate HP. Now in MOP it's not clunky at all, and seems to be well designed. The only real problem is that other classes have a lot of abilities that are thoughtlessly designed. Even Paladin talents have majority of concern given towards Holy, and Ret was an after thought.
If you look at the Paladin talent tree you'll see stuff that works best for Holy. Even Protection has a hard time justifying every talent, because it was built for Holy in mind. Like for example
Unbreakable Spirit.
Holy --> Being able to Bubble has 0 downsides for Holy. Cast heals all day long in a bubble. Especially Lay On Hands which just adds to their healing.
Protection --> Bubble drops threat for Prot so this does jack. Lay on Hands is probably the only benefit Protection gets.
Retribution --> Bubbling nerfs damage by 50%, so you won't want to do this too often in Raids. In Arena you won't live past the first train to generate enough HP to get the cool down quick enough to use it again. Lay On Hands in nice in PvE but when they make LoH immune to Tsulong it really limits its uses for Rets.
Overall this talent is made specifically for Holy cause using bubble has 0 downsides for them. Where as Prot and Ret have bubble work against them. It's a poorly thought out talent.