Last boss isn't that bad. Max stats. Focus on him and the spawn glyph he summons. Your partners take care of the zombies really well. Great game. Good UI.
Dart Wall and Spiked Floor, when fully upgraded, are the only traps you need to beat every level. But still had a great time playing. Can't wait for more.
Level 9 is not that bad. I beat it second try. Spam archers and you should be fine. Just make sure that by round 7 you have at least 2 archers on all 3 islands.