I've read through the classes in the new Player's Handbook. There's a curious change to how religious characters obtain their power. In previous editions of D&D, religious characters prayed to their deity or pantheon and received powers based on their faith. The deity or deities might be listening or might be distant, but the power gained came from the gods.
In 4th edition characters are divorced from their deities. They gain power from their investiture into the faith, not even from their faith itself. A deity becomes the religious characters fashion accessory. The character can defy the will of the deity, defy the will of the faith, or do whatever they want, but that invested power is irrevocable. I find it an odd design decision and I don't like it.
Meanwhile, wizards "tap the true power that permeates the cosmos." The warlock also taps into power from beings they "commune" with, either fey, infernal or alien. Don't get me wrong, I like the new designs of these classes, but why downplay the religious character? I can't imagine it's out of some concern over religion in the game, because honestly, this approach strikes me as rather hostile towards the whole concept of religion.
Paladins are no longer paladins. They're more like holy warriors from Player's Handbook II or Book of the Righteous from Green Ronin. There is no more paladins' code, no restrictions on association, and a definite step away from the pompous knight that nobody wanted to play (which is good). They must be the same alignment as their deity, even if it's unaligned. Paladins are also invested into their faiths, their power coming from ritual, rather than their god that they must follow in alignment so closely. But what if they don't want to tow the line? Their paladinhood is irrevocable, as neither the god nor the religious order seems to have any control over the paladins power once he's invested.
The investiture approach to divine power is one step too far for my liking. I appreciate the concept that a god might not be paying attention and that a follower might deviate from the straight and narrow (or crooked and wide, if they worship an evil god). I like that the high priest of the good god can be corrupt without some simple spell revealing his schemes. What I don't like is the divestiture of religious power from the game. It makes the gods and the heavens irrelevant and elevates the arcane and alien. It's a simple enough fluff decision to change, but I find it odd that the designers felt the need to do this and I wonder why.