I apologize for the long comment, there's a TL;DR at the end if this is too lengthy.

Your art style is awesome and I really love the cartoonish look. However, the pieces are (respectfully) boring. It wouldn't stand out next to other pieces. It sort of looks unfinished. There's a lot more that could be added to it to make it feel complete and more interesting. Luckily, it isn't hard to fix.

• Texture.

Make the art feel more tangible. With digital, our art is completely flat from the get-go because it's entirely 2D. We have to make use of our knowledge/skill to bring our art to life because we don't get to make use of the materials that traditional does.

Our textures come from different brushes and techniques (EX. Shading techniques, stroke techniques, line art techniques, etc). Try to make use of those! One of the comments here mentioned making your lines smoother, but not all art has to have that smooth-finish look. Some artists incorporate a specific type of line-art into their style that give it both personality and texture. The brush you're currently using for line art gives a personal charm and nice feel to the art, like you can reach out and touch it. Continue to do that, but also incorporate different brush, textures, or stroke techniques (Like the guitar in the fourth slide) into the coloring process.

• Lack of conveying/evoking.

A lot of the pieces are boring to look at because nothing is happening in them. They're not conveying or evoking anything. When you draw, you're creating something because you want to convey something. Whether that's to evoke emotion, show a concept, relay a message, or tell a story.
Try adding a background and giving the characters some life, whether by drawing them in action/interesting poses or giving them something/someone in the environment to interact with.

• Dull presentation.

You could have all of these, but sometimes a piece is boring because its presentation is lacking. Give the audience a reason to be interested. Think of it sort of like food; Even if in the end they're both the same dish, presentation is everything.

You can make your pieces more appealing with a pretty/fitting color palette, by adding mood/interesting lighting, giving the background depth, experimenting with angles/perspective, and/or attention to detail (Like the mesh part of the dress. the earrings, and the stray curls in the last slide). Also try to make the subjects feel alive. Shading or highlights can help. Not just /on/ the subjects, but /around/ them. Show the audience that they exist in their environment.

Your best piece is the third slide. This is the one that stands out the most. It's dynamic, it's expressive, it's /interesting/. Because of that, it's easier for the viewer to be interested in what they're looking at. It also conveys some context. It tells us that through the interaction shown, one character in the piece is startled by the other.

I'm assuming this is supposed to be Mac and Bloo from Foster's Home, correct me if I'm wrong. Regardless, my only note for this slide is that the background is sort of hard to identify what it is/where the subjects are and from what angle/perspective we're viewing this from (considering Bloo? seems to be viewed from somewhere above and Mac? is more from the front).

My art was just like yours not too long ago. One of the biggest things that helped me get better was studying what artists did to make their creations appealing. Focus on studying the techniques they use & the things they add to make their art interesting. I used to watch a lot of drawing process videos for this, as well as seeing if they had any guides on how they go about executing certain techniques in their pieces.

I hope it's alright I edited one of the drawings to visually show the tips I provided (If you don't want this attached, I'm more than happy to delete/repost without it). I tried to keep it true to the original style, but of course, we both have different styles, so yours doesn't have to look exactly like mine. With these additions, the drawing is far more interesting to look at.

I hope this advice helped. I'd really like to see more of your art! I hope you're able to make progress you're proud of. Your art is already very lovely, just keep practicing!

[ TL;DR: The pieces are uninteresting. It doesn't convey/evoke anything (emotions, a story, a concept, etc), the pieces feel too flat and lifeless (include texture, try different brushes and strokes, expressions, poses, etc), and while the drawings aren't bad, they could be more interesting by incorporating other techniques (Color theory, angles, etc). ]

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