Hiya.
I did a little math analysis to see how the moon druid fared against the barb, as they are both primal fighters using limited resources for raw awesome. You can find that there:
http://www.enworld.org/forum/showth...2nd-level-A-Little-Math&p=6405787#post6405787
The quick conclusion: I can see the concern. The key is the Moon Druid is roughly comparable to the Barb with just 1 use of wildshape. With 2 in a fight, they are significantly better...and we haven't even touched spells. And of course, that is just in raw power, that doesn't touch the wondrous flexibility that various forms offer.
Sure, numbers are numbers. But as Sacrosanct said at least twice above, and I think someone else as well...the "combat" is only 1/3 of the picture. That picture is also in a perfectly flat, predictable environment. Alas, 2/3 of D&D isn't about numbers and finding a perfectly flat, predictable environment in a fantasy campaign should be pretty uncommon.
How do the druids numbers stack up when he DOESN'T have any wildshape and the Barbarian doesn't have any rage left? You should do that as well, because the druid's wildshape will not always be viable, not always be available, and not always be sustainable. There are many detriments to changing into the form of, say, a brown bear. The key benefit is size/weight, senses, and hp/dmg. As a bear you can't climb a rope, use a wooden ladder, or, you know, speak. Anything with brute-force would be awesome though!
Also, campaign world stuff can get in the way of this "numbers game". Not getting to be able to actually take a short rest for one. Other stuff goes on in the campaign that may very well (and likely, IME) force the druid to change back to his original shape (human, elf, etc). As I said, perfect flat, predictable environment...wildshape may be a bit overpowered...but in the layered, chaotic surroundings that is a normal campaign? I'm not seeing it.
As a note, I have one player in my current Greyhawk campaign that is a Moon Druid. I already told him during character creation that the wildshape/HP thing may get a change if we find it too over powered. But so far (they just got to level 3 iirc), he's not OP at all. He (the player) always tries to have an exit strategy for every character he plays for when things go horribly, horribly wrong...so having one wildshape is his "ace in the hole" for when the TPK spotlight starts to shine down on them.

That said, he is also smart enough to realize that the party is tougher than his is alone...so using a shape to get some kind of advantage over his opponents (scouting a dungeon, flying over an encampment, luring some opponents away or into an ambush, etc) is a MUCH better option than simply turning into a bear and charging in. The most powerful aspect of the druids wildshape has always been (again, IME), it's utility and ability to be "ignored" (turning into a rat and hanging out in the castle to gather information....rats get pretty much ignored). That versitality is easily the most powerful thing going for a druid with regards to wildshape...not "the numbers".
^_^
Paul L. Ming