So I just want to make a mini-game to keep playing with Esenthel, and I'm having something 2D in mind.

How would I go about this? Does Esenthel actually have some settings for 2D games, or the best I can do is stop the camera from moving on all axes?

If you mean traditional 2D with sprites, you don't even need to worry about the camera. For this there are a lot of tools such as ImageAtlas that can be used.
If you mean using 3D assets on 2 dimensions, you can freeze x, y, or z movement in physics on objects, as well.

I've been doing some tests with 2.5D (3D in sideview) and everything works just fine. If this is what you want to do, let me know and I can share some code for the playermovement.

If you mean regular 2D, that's definitely possible. Apart from drawing images, you can draw all sorts of shapes that are included in the Esenthel Engine. You can batch these as well, so you can draw thousands of things at the same time.

I know close to nothing about 2D game design, so... I'm not sure what sprites mean;
So I could use atlas and basically have my whole game made inside the GUI?

Then I will have no Game World? Are there some settings I should handle to make sure I get best performance for 2D games, to avoid using anything I'd need for 3D to be more efficient?

To put it in an easy way, you can consider sprites to be just images. Generally though, they will contain multiple images within.

You won't be rendering your game as part of the GUI. There are a couple of things you can do.

1. You can go 2.5 D (2D in a 3D world). This simply means that you'll be using a 3D axis system, but you'll be focused on 2D movement. This way, you can still use the Esenthel Editor to create your worlds (Placing planes in 3D space, and you will spawn a camera that looks at these planes.). With this, you are faking 2D, since you are still drawing models (planes) with images on them in world space. You just position the camera so that you look straight at them, and control the movement so it resembles 2D.

2. Or, go full on 2D. You won't be using a 3D axes system. You will draw images in screenspace (Only x and y coordinates). You can also use the included shapes in the Esenthel Engine (lines, circles, rects, ovals, ...)

Most programmers that I know started with 2D before switching to 3D. Give it some research and you'll soon figure out how easy it actually is.

Thanks. Yes I suppose research is the right way to start, but I always did a bad job with that

The 2nd option is what interests me, and I was wondering what are some parameters that I should consider to make the game more efficient.

I would personally start by making a simple game such as Pong so you can get a feel for how the 2D works and how it's different from 3D.

That's pretty much what I'm trying; one of those "catch the thing that falls from the sky" games.

For all 2d games there are only Rectangular maths, so physics could simply be checked by w & h or center and radius for rounded objects.

If you know how to work with classes etc, you can literally make the whole players logic without one visible thing, because the image that you draw is only an image drawn at player's co-ordinates + size.

//If mouse is inside rectangle
if(Ms.test(PlayerImageRectangle)) BoomHitsThePlayer.

if(Ms.test(FallingStarRectangle))BoomCatchOneGold.