It holds up surprisingly well, compared to my other old games.
It's simple aestehtic allowed for rapid developement, but my lack of coding skills and experience led me to quicky run out of steam on the project.
If I were to remake it today, I would do a few things differently:
The enemies would have path finding abilities and would take cover and call back-up.
Friendlies would try to guard you, and perhaps a mechanic would be added to where you could order them around and arm them.
Enemies would not shoot randomly, and when they were about to shoot, they would have an anticipation animation.
The in-game shop would be clearer, and things would be priced better.
There would be more satisfying sound effects.
Proper boss battles.
A better visual theme with a limited palette, not just quickie tiny graphics.
Satisfying audio and visual cues for when you're out of ammo, you've picked up health, a friendly was lost, or the last enemy on the field was killed.
Proper music not lifted from other games ;)
Although that seems like the game is missing a lot, what makes it fun is already there:
The game-play is simple
The levels are quick and exciting
The environments have a good amount of variety
There are upgrades
You have little buddies that fight with you
Download Peg Soldier and try it out for yourself.
I'm sure I'll make a similar title eventually.