How does this title apply to Tower Defense games?
Well let me tell you.
The title is a perfect description of the quality of TD games out there.
I've played through many TD games, trust me. I've played more than one normal person should in a life time.
The good: There are only around 10-15 TD games out right now worthy of this category. And you probably know most of them if your a fan. Desktop TD, Vector TD, VR Defender Y3K, Xeno Tactic 1, etc. When you get into these games they make your palms sweat and your heart race hoping that you can survive one more enemy wave so you can buy that upgrade you've had your eye on.
The Bad: Here you will find a lot of games that tried to be "good" but just didn't make it. They often look great but play badly. Not enough time and effort was put into balancing the difficulty, game play, and mechanics. Making for either a very mundane boring progression, or the opposite which is a battle that starts and ends knowing its completely hopeless.
The Ugly: Here you have the bottom feeders. Not really worth being associated with the others, but just get thrown together by association. Here its usually a toss up as to what's worse between the graphics, game play, or lack of anything unique or creative.
Thankfully "The Good" make up for the rest.