Let me start by saying- I think the healing is really fun. I have not had this much fun healing since vanilla. I love that the avoidable damage is just devastating, while the regular damage is healable. It really highlights the responsibility of the group to mitigate damage wherever possible.
With that said- I am very unhappy with holy healing right now. Disc healing is quite fun... but the extreme mana problems with holy make the spec a drag. I find that most of the time I feel like I am spamming a huge set of weak heals, and fighting with mana to stay afloat.
Summary of my complaints with the spec:
1. Spells are too expensive. Using a huge toolbox of expensive spells drains mana quickly (even avoiding flash heal).
2. Spells are weak. The huge toolbox is a detriment when the spells are individually weak. It requires more casting to keep up with damage. Example of a weak spell: Circle of healing. I find this spell to heal for an incredibly small amount relative to scaling health, and I use PoH and other heals if I actually need to move a health bar.
3. Reduction in fun due to less use of good mechanics. PoM is one of my favorite spells in the game. The increased CD, due to loss of divine providence means less use of a fun spell and less fun. CoH used to be kind of fun (post nerf)... but with the longer CD and weak strength, it is really not very fun, imo.
4. Chakra- This is a complete stumbling block for the spec. When I play disc or other healers, healing is now challenging enough without having to micromanage a mechanic to make the most of my spells. I REALLY REALLY feel this mechanic is obsolete. In Wrath, holies were the versatile healer, and I could see t his mechanic being used to make the most of a diversity "niche". Now that all healers are versatile, I really don't see the reason for an additional burden on the holy spec.
These are my feelings so far with holy. Put simply, I think the spec is overburdened with inefficient spells that, while novel in concept, have little practical impact and are causing the more useful spells to be too limited for balancing purposes. I think the mana management of the spec is less about management and more of a drain.
I really enjoy healing in Cata, and I am incredibly surprised at how great of a job devs have done with the new model. I have a great time healing with disc, druid, and even my pally friend is loving healing. (I haven't tried shaman). Holy is, at this point, just glaringly weak when compared to other specs, imo.