Fun, this game is way better than the previous one which I found frustrating. Finding the side quest jewels was a little tedious. Don't forget to upgrade your speed which helps you get more efficiency out of your fuel.
The only way to effectively deal with giants after level 6 is to upgrade your hero's attack to max it seems. Once I did that I was actually able to pass levels again.
I managed to complete warpath and divide. My hero had a full upgraded talent tree with 30+ base damage and 30+ firing rate. Here's how I did it:
Warpath: 30+ waves only. I used only my here for this one. Place him in the middle of the map. Add a scouting post and a battle standard for him. As the waves progress add some power totems. He should be doing around 200 dmg per hit. This should be more than enough to get you over the limit.
Divide: +30 waves, +double enemies. Place your hero 2 spots above the vantage point so he covers the exit. You may want to give him a scouting post. Build 5 guard towers along the top of the island side by side attacking the exit. This may take a couple of waves. Upgrade them all to shock towers. Use frenzy liberally to stay alive until the towers are ready. Add battle standard when you have some extra cash. The overkill damage is enough to get you to 250k.
There seem to be some cards in the standard pack I just can't get. I've bought around 30 gold decks now and I keep getting the same ones. Give me my Freddie dammit!