There may be a degree of undercover cop lurking within me. However, as an undercover, I say nothing, but learn from others, be it perfection, a happy little misfortune, or major misalignment. If I find something, which, in my mind, is disagreeable, I ask myself what I might have done differently.
Colors are definitely individual choices and often depend on fabric availability, so is often a non issue. However, I see things which would not have been my choice, but in someone else's quilt - the choices and combinations work. I make mental note not to dismiss that as a possibility in my future.
Pattern will showcase a technique. Mental note to self: gotta get that one; or, good one to keep in mind; or, I'm not ready for that one; or, GOOD GRIEF! Makes me dizzy, Good for that quilter who spent the time and effort. Are they still sane?; or, nice pattern, but I think I may have modified that by adding cornerstones or stashing or ... to break up that concentration of color.
Technique: Poor alignment - note to self, remember to pin or glue; wobbly seams - been there, done that, remember to slow down; block upside down or wrong side out - Oops, no need to unsew the entire row, here's how to recover. (ask me how I know).
Multiple problems on an experienced quilters project: We are our own judges, and are more critical of our work than anyone else. They have probably already kicked themselves, and are looking for a ray of sunshine before donating the quilt to the animal shelter. So I think, "Was the quilter in a big hurry? Why didn't the seams get pressed?; Wow, look at all those puckers! Was this a failure to pre-wash?; Adam 12, where are you?