These are the parameters that I use to judge knives, and are based on my preferences. They define what I consider to be a good knife, and they don't make for a quick and easy way for anyone to tell good knives from bad ones.
Blade shape: Practical. No exaggerated upswept tips, extreme recurves, compound grinds, or serrations. Points lost for blackened blade if the steel is stainless. Additional points lost if the blade stock is overly thick or the blade is extremely wide.
Blade steel: A quality stainless steel with a proper heat treat. 154CM or better at 58-62 RC. Bonus points for extreme corrosion resistance.
Ergonomics: 4"+ handle, especially with some hand-filling curves and a well-placed finger groove. Blade should be easy to open and close one-handed rapidly when necessary. Very difficult to judge without handling the knife.
Handle material: No cheap plastic or steel. I like titanium with some texture best, but synthetic and natural handle materials can be nice as well, if they suit the knife.
Fit and finish: Fit should be so tight as to make the knife difficult to assemble/disassemble. The blade should be perfectly centered and absolutely free of play. Action should be totally smooth with no hang-ups, at least after a break-in period. All edges should be radiused/chamfered in some way so as to avoid hot spots. Bonus points if the blade spine is radiused as well.
As you might have surmised from these criteria, I'm a big fan of Chris Reeve knives. Many of the features I look for are hard to find in cheaper knives, so I've reworked my very limited budget to accommodate knives I can get excited about. I used to buy a couple of knives a month, but now I pinch and save and only pick up the ones I know I'm going to love.