Brushes are never uniform?

All I use Illustrator for is to make illustrations; nothing more. I'm no expert; I took a class in highschool once but only remember the basics.

With that being said, I had been drawing a comic strip for fun. I had multiple artboards open so I can refer to each one as needed.

One day, I noticed that all of the brush strokes looked funny (n ALL the open artboards), I thought maybe I had selected a different brush definition but as I tried to change it, I couldn't get it back to what it once was.

Even if I start a new drawing, the brushes I normally use will look like this. Not sure what I did but I'd like to have solid lines and not this fuzzy ones.

Here's some screen shots..

Here's a stroke up close..

I normally don't mess with any settings I'm not familiar with so I'm not sure how it happened, but I'm unable to draw with solid lines now..

Please help, I miss drawing!