-Get rid of baby headcrabs. The babies are faster than fast headcrabs and are more dangerous then them since they are hard to hit and don't have to walk away before attacking again and are way too hard for a level 1 jumping piece of bread.
-Get rid of vortigaunts. Undodgable attacks are fine in areas where there's room to take cover, which there's not much of where they spawn.
-Make the shop keeper inside the house so you don't have to exit out of the shop every time something spawns around you.
-Up the damage on the manhacks. They're completely useless.
-Give the sword some swing radius. Also a crosshair would be nice.
-Make a character system for having multiple characters.
-Mana regen should be upped. It's waaaaay too slow.
I'll edit this if I think of any more.