I like idea about showing the timer. I don't implement good old timer because I want to add visual explanation of why a player loses. So I think I make timer + endless wave + hide bonuses when strong enemy come.
"I don't implement good old timer because I want to add visual explanation of why a player loses."
This explanation looks silly, to be honest. "Oh, no, piece of junk that we call base was destroyed! Guess it's too late to steamroll these dwarves with hordes of ogres that we have."
