This is really great! You made the right choices for this to be good, the slowly recharging health bar makes the game feel a lot more fair, and it makes it really epic when they whole tower suddenly crumbles. One thing that would improve the experience a lot I think are some nice collision SFX when blocks hit things at a high enough velocity, it could be really satisfying. (Also I love the MS paint aesthetic you went for, it fits really well)