Finally made a video:

This doesn't have the terrain showing, I figured out it is quicker to make a build with terrain switched off, and it increases the filesize quite a bit so I might drop the terrain, not sure yet.

I put in support yesterday for more than one enemy type, I have got a third type but haven't put in yet. These will have different strengths / health / speed. Also spent ages debugging yesterday from a nasty c# references bug, first time I've had to do any major debugging and it was difficult because I only have debug.log statements to rely on, as yet I have no debugging in monodevelop.

The reason for the bug was because I'm using pooling for my game objects, so as not to new and create unity objects, they are just reused and position and visibility switched. So I have an intermediate 'reference' (another reference!) actor which stores which pooled actor of each type in is an actor slot. This makes it slightly more complex the adding and deleting actor code. Anyway when deleting an array element, I switched the last array element with the one to be deleted, then decrement the count. However, in c# the = operator does not copy the data like in c++, it copies the reference, so all kinds of unpredictable behaviour was resulting. Anyway, bug solved, crisis averted!

I also put in some basic auto cameras. They work pretty well. There is an overview of the whole board, which does not change, a follow cam which zooms in on a particular actor, and an area cam, which treats all active actors as an area to focus on. The follow cam actually follows a point just ahead of the actor, because there is a delay from the smoothing. The area cam needs a little tweaking to get better. 

Next I need the other enemy type, and different tower types. And I need to put in a special big building or something for your base, maybe with some particle effects to show it being destroyed.