The most time consuming part has been the animation, but that's no surprise because I have no experience doing it. I've been doing a combination of paper doll animation for the monsters and frame-based animation for the effects. Fortunately, it took half the time to animate the troll than the skeleton. The skeletons are built from MovieClip body parts, so I can randomly give them variation. Likewise, the troll can be changed to an ogre by setting each body part to frame two.
Bazooka: Shoots further the longer the cursor button is held. Explodes and does radius damage. Can be upgraded to leave a flame behind for a couple seconds, and then upgraded again to shoot baby rockets into the air on impact.
Bow and arrow: Shoots further the longer the cursor button is held. The arrows stick into the enemies or ground. I'm thinking of it being upgraded to shoot multiple arrows, or poisonous arrows, or both. The red skeleton just got hurt (I didn't bother with pain animation sequences).
Rifle: Does more damage the longer the cursor button is held, and the laser gets brighter, just like the sniper from Team Fortress 2.
I want at least one other weapon, so it might be an uzi that gets less accurate the longer the button is held down. The protective wall can be upgraded from picket fence, to tree trunks, to bricks, to stone.