I've seen you playing this a few times. I tried it on mobile at some point but didn't get into it. I'm definitely going to give it another shot. Tower Defense is one genre I'm really passionate about, but I have pretty high standards. This being a paid game definitely makes it better for me because there are a lot of trash mobile games in this genre (possibly because it's fairly approachable from a coding standpoint and doesn't require AI).
Defense Grid is my favorite of all time but a unique spin on the genre was Anomaly: Warzone Earth. It is kind of reverse TD as your 'towers' are vehicles in a convoy and you have to plan the order to place upgrades etc and sometimes frantically try to repair them. Instead of protecting a static location your vehicles are on the move and the goal is to get somewhere while "aliens" have put menacing towers that you need to get past. It's a pretty good game, but I don't know if it has pause functionality or not.
I actually made a walkthrough to that game but I am afraid I may have deleted it... welp.
