Let's see how well this thread holds up!
We've got lots of threads here with various sides arguing the merits of read noise and banding in files, fixed pattern noise (FPN), dynamic range (DR), some on annoying lens aberrations and plenty more.
INSTEAD OF RE-HASHING THE TIRED OR UNFINISHED ARGUMENTS, POST YOUR IMAGES HERE THAT SHOW THE FLAW THAT RUINED THE SHOT FOR YOU.
If it's subtle, tell us what it is (and where) versus what you hoped for or expected.
Avoid posting images that started with poor technique or other major problems that are user errors rather than equipment flaws. If you were close but couldn't fix it in post... Show before, after, and describe what you wanted to achieve.
We have a lot of good people with good advice on good equipment here. A BIG HOLE IN THE INFORMATION, in my opinion, IS WHAT ARE THE WEAKNESSES OF A PARTICULAR CAMERA OR LENS or other bit of equipment that can make it impossible, difficult, or frustrating to get the shot you wanted.
LET'S SEE THE BAD STUFF SO WE CAN LEARN TO AVOID IT OR WORK AROUND IT and not miss any more shots because of it. I, for one, had been a little too remiss in the past and I accepted of a lot of positive reviews on equipment only to find out shortly after buying and using it that it had some significant flaws that hindered its usefulness to me.
POST YOUR REMEDIES OR WORK-AROUNDS. If discussing the issue, please EDIT YOUR QUOTING TO MINIMIZE THE QUOTE TO ONLY WHAT'S REALLY NEEDED instead of quoting everything including all the graphics.
Let the bashing, and learning, begin!
Have fun, keep it civil, make it EDUCATIONAL.
Addendum - to give you an example, here's a scaled shot taken with a 5D Mark II and EF 70-200mm f/2.8 L IS II
The image is basically ruined by garish, multi-outlined bokeh. This is not a crop, this is the full frame.
200mm at f/4.0
hasty typo fixed, supposed to be 200mm, not 20mm.