After all these years, and growing up with Windows 3.1, I have seen an entire evolution of computers and software. Touch screens and large resolutions were a pipe dream just 15 years ago. Now it's the norm. Going from a Packard Bell (yes, before HP) that couldn't run 3D Ultra Mini...
Remember to make the lizards take the longest route you can when you put down your towers.
You can see the routes flying units take, so make sure they're covered.
Sometimes, it's worth upgrading old towers instead of buying new ones.