I am just good enough at Tower Defense games not to fail immediately, but I never seem to have the skill necessary to get through them entirely. I have always prided myself on long-term planning, as I grew up on RTS games and kicking some serious ass against other players by out-planning/out-smarting them.
But then Warcraft III came out, and through BNet, Wintermaul was born. I fell in love with this custom game, and along with LoaP, this was one of the games I played the most. But as much as I loved Wintermaul, I only ever really had about a 10% success-rate. With later iterations that involved sending waves against players looking to fill your spawn and overwhelm your team, my success-rate dropped to around 6-8%.
And that has been my story with other TD games, too. Hell; even the Steamworld TD on the 3DS gives me trouble, and that is simpler/easier than Plants vs. Zombies. Not sure if I have some sort of mental-block when it comes to TD end-games, but I still love them to death, and regularly play them.