I wouldn't put it that way, the low ISO dynamic range, compared to many competing cameras, is that bad as they say, but otherwise it is good, only the D800 has more MP, at high ISO it does about as well as the rest of the best the D800 and D4. It doesn't have the 36MP reach/max detail of the D800 and it has far less low ISO DR (which is a shame IMO) and the color array filter makes it a bit more color blind (this latter aspect hasn't really been studied to see what real world effects or not it produces other than the chroma SNR won't improve as much compared to the 5D2 as the luminance SNR during natural outdoor lighting temps, indoors it has about same color as all the rest though) but otherwise every other DSLR made is basically the same or lower MP count, all but less than a handful have worse SNR.
So the IQ is mostly very good (about tied for best luminance SNR, about tied for best MP other than for one DSLR, not quite the best but pretty high up there chroma SNR, about tied for the best in terms of lack of high iso banding) other than it has sadly fallen way behind the best in terms of maximum dynamic range, even a stop or more behind the best non-exmor sensors (and the low iso banding is still worse than on some and it's a bit more color blind, but the latter it's very tricky to figure out what it means real world, it would need lots of complex testing).
So no the IQ is not as bad as everyone says, or more accurately everyone isn't saying it is bad, what some are saying, myself certainly include
, is that the dynamic range at lower ISOs is fairly out of date and a bit disappointing. For the shots where that doesn't matter it's right up at or near the top though (ignoring metamerism index).
Overall no, for dynamic range yes (Canon really does need to get caring about the latter and realize they are getting trounced there and that they have long fallen off their king's perch).