Factorized

A side-scroller video game about getting revenge on an evil AI by fighting your way through their factory and destroying their machines!
Equipped with your various instruments of vengeance, shoot, drill, and explode the various robotic (and non-robotic) adversaries that stand between you and The Reconstructor.

And now, let's meet your arsenal.

The pistol - Your day one. It's accurate, but is quickly out-DPS'd by:
The shotgun - The go-to weapon. The one that does the vast majority of close-range damage. That is, unless, you mean within one hit. That would go to:
The Drill - Your pocket nuke. If the shotgun isn't doing the trick, then this is your best bet. As an added bonus, it completely negates any kind of shield or healing radius, making it great for the enemies that just won't die. And finally, the fourth weapon:
The ______ - Oh... Yeah that one's a bit of a spoiler. You'll probably like it though. It's a bit gimmicky, but it has its niches where it outperforms any other weapon.

Included with the game are:
The aforementioned four weapons

Two unlockable movement abilities

Five main bosses + an additional three hidden extra ones

Two endings

Five main areas to explore + two hidden ones

Two starting difficulties + two unlockable ones

A bunch of steam achievements

Four additional gamemodes separate from the campaign

A 24-song original soundtrack

-And a partridge in a pear tree (not present in-game, but is totally waiting just outside the starting area)

Wow! That was a pretty short description...

I wonder if there's anything left to discover that wasn't mentioned...

Hmm...

=]