Or you could have maked some Metroid like sections also !
Some HUD seems really from Halo ? if nojt it's very well copied.
(something to avoid fi you would go commercial one day with this game ) !
If you don't target to animate ennemies, you can even use 3D models !
Or make minimal animations like this sort of retro RPG game :
Dot Game Heores


Would be retro ans stylized also !