I had played the game today for 5 hours managing to arrive to wave 10! and I must say that I've enjoyed all the time.
The idea reminds me Kingdom Under Fire a game that I loved in the past, anyway I want to say what should be improved:
1) Demolish building don't give you back some resources
2) The combat system is clunky as hell often the hero get stunned getting destroyed
3) If you lose Royal Gards you cant rebuild them
4) The hero should level UP like all the other units
5) The reward system is unfair because you can use it only when you restart a new game.. I needed my new giant and the abilities I've unlocked to survive.
6) You shoud be able to build on top of trees!
7) Why I can't sell in the market extra stuff like armors and weapons, or buy needed resouces?
8) The fallen king and his bodyguards are too strong imo
9) The building are too squishy and since the enemy can use catapults I would like to see something like only catapults can destroy buildings like castles and defensive walls
10) why catapults can shoots while in melee combat?
Ten list points after 10 waves not bad! I'm sure you'll do a great job making this game great.