So I Finally Took Time to Make a Game

The author mentions a lack of a sensation of speed. The main reason for this is relatively obvious if you spend a few moments examining the gameplay footage: The sprites all have a simple traditional 2D drop shadow, where the size of the shadow is the same as the size of the sprite and it's offset by a few pixels. This visually implies that the sprites are very low to the ground, and as a result the slow scrolling speed of the background means that the sprites are not moving very quickly.

Under normal circumstances the cloud layer (moving at a higher scrolling rate - parallax) is a good way to create a sense of motion, but it's really just making it look like the cloud layer is moving fast :) What you really want is to fix the way you're shadowing the objects.

Removing the shadows entirely would probably eliminate the false cue but then you lose a sense of the sprites floating over the terrain.

There's also a related problem in that the player and enemy sprites are effectively floating on their own layer that doesn't scroll. When the enemy sprites are flying along at their own pace this is easier to ignore, but when an enemy appears that isn't moving horizontally at all (or is aligned with a fixed point) it makes it more obvious that the depth and motion cues are wrong.

To be fair, these are all problems that you will see in other games of this type. It's worse when you're using a straight-on top-down perspective like the game in this post.

EDIT: Some relevant examples:

Raptor: Call of the Shadows is an old 2D shooter with a similar perspective (top down), though scrolling vertically. This game does shadowing relatively correctly, where the sprites cast shadows directly on the background layer at a position that scrolls with the layer - so as the sprite advances down the screen, the relative position of the shadow changes. This creates a sense of the sprites and the background scrolling at different speeds, so you feel some depth. (The shadows are nearly as large as the sprites, though, so it still doesn't feel like they're very far off the ground.)

https://www.youtube.com/watch?v=grXkzisSEM4#t=7m30s

Ikaruga takes an alternative route here: While the enemies are basically 2D objects on a flat plane, they don't cast shadows at all and the backgrounds are effectively just FMVs containing various motion. They use the background to convey a sense of camera motion without tying objects to them at all. This lets you avoid having to precisely align the sizes and positions of your entities with the background (though of course, they end up kind of disassociated)

A "sufficient" shoot'em up it's not too complicated to make, you can get an OK-ish engine in a week, but then you have to add content (stages, enemies, different AIs, etc). IMHO hat's the main difficulty of the genre, because a lot of work is required for just a few minutes of gameplay.

I've made myself a couple of these games and they're fun to make, but it's not too rewarding (eg, I made this one in a month: http://www.usebox.net/jjm/flax/ -- and it's ~6 minutes to get to the end of the three stages).

My partner and I spent three years making our own 2D game engine and game as well: http://junkyardtom.com

It took so long because we initially built it in ruby, but found it was too slow; then pascal but found out it wouldn't work so well on Android; then finally Java.

It's also not a shoot-em-up -- there's a fair amount of logic involved in the movement of the actors (some rudimentary AI) and way too many game rules. Maybe we should have started with a shoot-em-up...

We're going to release the engine some day (when we have time to clean it up) -- it uses XML files to configure all of the actors and the 'stage' so maybe it will be useful to teach basic parallelism to kids or something...

The articale reminds me a bit of this "Juice it or lose it" talk by Martin Jonasson and Petri Purho.

https://www.youtube.com/watch?v=Fy0aCDmgnxg

I've also made a shoot'em up game last year december in a day or 2 to celebrate the silliness of Doge Coin.

I did make use of the moving background to increase the sensation of speed when speed power up is taken( Eventhough i know the background should not be moving at all :P)

http://tensaix2j.github.io/tothemoon/

Anyway.. Just to share. Have fun.