If you meet any of the following conditions, you have failed:
Your lights are all one colour
You might think that uniform colours look really IN and DESIGN. I think uniformity is contemptable and that designers need to relearn their colour charts. Seriously, guys, there are more colours out there then white, grey and black.
You have blue lights
The blue lights that came out a few years ago are the colour of death. Where Christmas lights are normally gay fun things, the blue lights suck fun out of your hearts, leaving only sorrow and loneliness.
You only have blue lights
What are you, a 16 year old goth girl who thinks all life is suffering and misery? Did you hire a Dementor to do your decorations?
Your lights are flashing
I could go with an epilepsy joke here but it isn't fit. What I hate about flashing lights is that they aren't random. They have a steady duty cycle, but each controler has a different duty cycle. This means every once 4-5 minutes or so they all sync up and this distracts me to no end.
Your lights imitate icicles
Not only because they are probably all white, but also because real icicles are an annoying sign your roof insulation needs to be fixed.
You don't have enough lights
A half-assed effort looks half-assed. Is half a Christmas going to be fun? Half a Christmas tree? Half of the plum pudding? Half the bottle of rum? OK, so that last one would be fun. At least until the next morning.
You have far to many lights
Even if having your front lawn as bright lit as a prison yard pleases you, please think of our telescopes, vital to the national interest and how light pollution is rendering them useless.