I've never really seen the big deal about angled/centered weapons. I can understand having hands that correspond, but what's wrong with having centered and angled weapons in the same wad? It's not like a real person would hold all his weapons pointing straight forward.

That is somewhat true, but the inconsistency of angled/non-angled weapons in the same wad can be just a bit bothersome, I will admit...

Unless you're going for the whole ironsight thing, where you have angled weapon sprites and centered sprites for the same weapon, the centered sprites being used for when you aim the weapon using the iron sights... then it's not really a problem, but I don't see many weapons that have angled and centered sprites for them at the same time.

The angle should really just depend on the weapon. For example, a shotgun shouldn't be angled, but an RPG should (over shoulder).
I really like the angle of the tommy gun for some reason.

Well, the Tommy Gun (which is the only angled weapon in the wad) is only slightly angled, so I hope it's not too big of a deal.

The first frame of my new monster is mostly done, I still wanna give him full sleeves and gloves because it wouldn't make sense to have the arms exposed on a radiation suit. I've tried creating a still, motionless actor that uses the first frame, but, even if I include the pictures in the wad file, it's completely invisible in game. Does anyone have a way around this? It's definitely not a problem in the DECORATE file.

Do you have the sprite offsets set correctly? If not, it's possible he's being displayed way off-center, and getting clipped into the floor or ceiling or some such.

Sprite offsets? I don't even.... I did notice that you could change where the sprite was placed in the WAD, that's what you mean, right?

EDIT: I figured out the controls, still trying to position it right.

No; sprite offsets determine where a sprite's visual representation is located relative to its placement in the game world (or, in the case of weapons/HUD, relative to the player's field-of-view). If you open up any given WAD in SLADE3 and examine the sprites, you'll notice they usually all have offsets. You'll need to give similar offsets to your sprites in order to make them appear correctly, since they don't have offsets by default. You can do it manually, or you can use SLADE3 to automatically apply offsets to a group of sprites at once.

I messed around with Slade3, still can't get it to show up in game. When I set the drop down list to "Sprite" it's right on top of where the lines meet, but it still won't show up in game.

Hmm, hard to say. Why don't you send me a PM or something so I can help you debug it without cluttering up this thread.