Thanks! Glad that you enjoyed the gameplay. Our pre-release testing indicated that some people thought the game was too easy and others thought it was way too hard/chaotic, so it was a challenge to balance.
The '4' was 'unarmed' combat which always applied the STUN effect. The idea was if there was a cluster of enemies of differing types you could more safely stun them all then maybe take a step back and surgically pelt them with projectiles. However, I don't think we had enough time to really introduce (and balance) that kind of strategy layer. Hopefully in 2.0.
And yea, the first couple levels were designed to ease the players in. Glad you enjoyed it!