I just took a few test shots with YN-622C triggers and my YN-568EX (I usually use them in M, so hadn't thought to test eTTL function), and with the single speedlight, if I had wireless and groups on, I was getting consistent underexposure. If I turned wireless off, eTTL exposure was spot-on. I did NOT get inconsistent exposure or missed fires. I also tested with my 580EXII as master unit (I have a 50D, so my pop-up can't act as master), and that worked ok, too. My YN-568EX is really no worse-behaving than my Canon 580EX or 580EXII in this regard. eTTL, as with any metering-based autoexposure system, can have variance, may not be spot-on, and can be annoying, but it should usually get in you in the ballpark. And wireless (in the proprietary optical system) or on-camera should not make much difference.
Just to cover all the bases, for the misfires, make sure that you're waiting until the flash recycles before pressing the shutter button. Use the recycle beep to notify you if you're not sure. Weak batteries might also cause an issue here, if it's taking more than 3s to recycle between bursts. This could also account for fluctuating power levels if the flash hasn't fully finished recycling before you fire it off again. Check how your FEC is set, as well, and make sure that your settings are kind to your flash. The YN-565EX is only slightly more powerful than a 430EXII--if you're trying to shoot in the dark at f/16 and iso 100, you're probably popping off at full power and you may still be underexposing. Speedlights are the low-end of the power range, flash-wise. Recommend iso 400 and f/4 as starting points.
It is not my experience that Yongnuo gear in wireless eTTL is a total shambles. However, I've read enough and researched enough about Yongnuo gear to know that early adopters of new models immediately after they've been released may end up being inadvertent beta testers. The 565EXII was only released earlier this month (June 2014), so that may be a contributing factor. There have also been reports than the YN-568EXII has issues with eTTL (it supposed works better in Average than Evaluative), and the 565EXII may have inherited that, if they're sharing components/design.
You might want to consider returning it. Yongnuos are cheap for a reason. There are reasons to pay more for OEM gear. IMHO, Yongnuos make great 2nd, 3rd, and 4th flashes (especially if you're going for the simplest manual-only flashes--less engineering to go wrong), but for a first/only flash, it may be worthwhile to save up a bit more and get an OEM unit.