BUG ALERT! First, I successfully equipped lv.5 equipment as lv.2 by selling all other equipment of the same type. Second, when selling the last of an item I had, specifically shirt, my item count dropped to -1 and asked me to refresh page. Since then the game has failed to load. gave it half an hour to try.
A few serious issues. First, towers should prepare next shot while waiting for enemies to get inside range instead of fire rate cooldown only going while enemies are in range. Major and possibly related bug: Towers, particularly artillery, have a bad habit of ignoring enemy groups completely. On third level, I put artillery at the spot closest to the start, and half the time it would let enemies most of the way past before ever firing on them.
Something reset my options on me, not sure what. I've been playing on Epic, got on today, and after about 2 hours of playing, checked medals and realized I got switched to default settings, which met normal.
@auzziegil: There is a hill near the bottom at the first u-turn. Placing your mortar on it allows it to one-shot all incoming spiders. You then need to get your mortar truck near their factory or wait until they run out of money. Hope this helps.
Sadly, a bit broken on my computer. Removeme doesn't ever slide. It digs its front end into the ground or just jumps on top of my word, making 18 impossible. I only beat 16 with luck. Yes, I did check the walkthough, it's not working for me.