That could definitely be the case. How do you usually go? Do you upgrade one thing throughout, or do a mix? I was trying to do a mix. I also sense that my strategy is not as good as it could be.

*edit*
I'm definitely not upgrading correctly, and I think that has the most to do with it. One game I tried ONLY upgrading the darts, and I lasted two about 3 waves. This last time I tried upgrading more strategically, and got to the laser beams