I'd hesitate to call the ipad 3 bad. It's still good (on iOS 7), its simply the Air series is that much improved.
It is all relative.
On the iPad scale, the iPad 3 is by far the worst iPad. It has the least amount of power-per-pixel than any iPad except the iPad 1, but unlike the iPad 1 it didn't have the "most magical device in the world" halo for early adopters. It had the shortest shelf life of any iPad for a reason, and it is my favorite example of how blind buying iOS devices in the expectation that they are all good and the specs don't matter is a way to get burned.
But compare the iPad 3 to my Transformer Prime that I bought a few months before and it was a great deal. The Prime is already abandoned- they stopped updating it at 4.1 or 4.2 I think-and even if I manually upgrade the OS with CM there are huge design flaws of terrible eMMC and the fact that the wifi is crippled by an aluminum cover. I paid iPad prices for that thing and it was a complete disaster. The iPad 3 would have been a steal in comparison.
In all honestly what we should be doing is praising the iPad 2. That thing was shrunk (iPad Mini) and leaped (when it was there alongside the iPad 4), but still sold in some form for years and still runs a modern version of iOS today. It will be a mobile device that gets the five years we expect out of a console or regular computer cycle, all in a form factor that hasn't been beat (I mean 10 inches is still a bigger tablet). It is a miracle.
The iPad 2 is what got me to buy the iPad Air 2. It was pretty obvious back in the day the iPad 2's SoC (especially the GPU) was a monster compared to anything else at the time including the weak iPhone 4 that was selling when it launched (or my Prime). Seeing as how the iPad Air 2 has such a beastly SoC it probably will be the next five year iOS device, and I think by the time it no longer runs the current OS the form factor will have finally changed.
Next generation when we get an iPad Air 2-level SoC inside the iPhone 6+S it will be a device that will be very hard to beat, very tempting. I am shocked we aren't there today actually, and that is why I think that today's iPhone 6+ will be the iPad 3 of the iPhone line. Power-per-pixel matters.