Don't worry, I love it when people give me feedback that's honest and constructive, so I thank you for taking the time to write this up.
To address some of what you said. No, currently you cannot connect to more than one tower at a time, but it was a feature I wanted to get done, sadly though, not enough time. The goal was to have upgradable towers and an upgradable battery. Upgrading towers would increase their damage and speed, while upgrading the battery would give it more power, therefore more connections to towers. The aiming/priority for the towers was not finished as I was going to refine it a little because I agree, that sometimes towers don't target what seems most important to target, again just not enough time.
Some things I'd like to ask/follow up with your feedback. I don't think that adding a hit stop/screen shake would be a good idea, to be honest. Why? Let's say you are using the electric tower that shoots around 10 times a second. You will be pausing the game briefly every1/10th of a second and that seems way too annoying. The same goes for screen shake, your screen will always be shaking. I personally don't think it fits into a tower defense game because those effects are usually for combat-style games.
Could you clarify what you are saying in your second paragraph? I think I understand what you mean by "remembering what was the last selected tower", but when you say "rather than pressing LMB to remove the tower and selecting the tower again and then adding it to a new place", I'm not sure I follow. You don't press LMB to remove towers and I'm not sure what you mean by "selecting the tower again". Also, dragging a tower from spot to spot takes away the thinking required for where to place a tower in the most efficient spot, therefore also having no point in having a currency system since you wouldn't have to sell towers, only reposition them.
I really like the slow-mo idea, I think it's perfect for the fast-paced game that it is, to slow down time while placing a tower because I see no reason to punish the player for trying to purchase a tower mid-wave/level. Thank you very much for the suggestion!