I really liked Sol Survivor and you probably will too if you like Defense Grid. DG is the better game by far, but that doesn't mean SS is bad. SS is more your typical tower defense game, point A to B, no cores. But it very much is styled like DG and the towers and such are pretty fun.
Excellent, excellent; Thanks for the recommendation. I wanted to wait on Toy Soldiers because, currently, the developers are removing the GFWL DRM. (From what I understand, users will be able to choose between the two versions of DRM.)
I have passed several times on Plants vs. Zombies, despite the craze it caused. It may be Tower Defense, but the demo always left me with negative feelings. The most glaring is, of course, the lack of graphical options. Despite getting an HD remake on mobile devices, the PC version has remained relatively hideous. (Relatively.) I like my Tower Defense games, but I feel more effort could have gone into the presentation of Plants vs. Zombies.
I await other CAG's to tell me how crazy I am. To a certain degree, I agree that my reasoning is a bit flawed, but, when it comes to Plants vs. Zombies, I end up "going with my gut." (A rare occurrence, to be sure.)