When comparing PICO-8 vs GDevelop, the Slant community recommends GDevelop for most people. In the question“What are the best game engines for point & click adventure games?” GDevelop is ranked 6th while PICO-8 is ranked 38th. The most important reason people chose GDevelop is:
The whole interface is intuitive and easy to learn: each part of the game can be designed using visual editors. The objects editor is used to create the objects of the game, the scene editor help you to build the levels of your game and the events editor allows to give life to the whole game without programming.
Specs
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Pros

Pro Takes away the pain of having to wire things together
Because it's an all in one product, you don't have to worry about things like how to load sprites.

Pro Very simple programing language
It's lua with a few modifications.

Pro Encourages building simple games
As a beginner it's all to tempting to try to make the games you like to play, like Zelda or Call of Duty when we should probably be making pong.
Pro Restrictions of tokens count "forces" to write code effectively
When you reach 8192 tokens, you're screwed. However, this limit can teach you to take a look at entire code and think how you could optimize it.
Pro Possible writing code in external editor
Since launch of 0.1.12c version of software, you can now write and include external script using the same directive just like in C / C++.

Pro Perhaps one of the easiest sound editors around

Pro Share the game in a .png file with other Pico-8 users

Pro You can read the code of any game you play

Pro Lots of examples
Almost every game made for the Pico-8 is open source (if you can download the .png, you can see the source).
Also there's the fancy Pico-8 "fanzine" that has lots of code examples as well as other great tutorials in a beautiful physical or PDF form.

Pro Easy to get things going very quickly
Pro Easy to use
The whole interface is intuitive and easy to learn: each part of the game can be designed using visual editors. The objects editor is used to create the objects of the game, the scene editor help you to build the levels of your game and the events editor allows to give life to the whole game without programming.

Pro Free and open-source
GDevelop's runtime libraries are MIT licensed. It can be used freely for projects of any type and there are no royalties associated with publishing games developed with GDevelop.
Pro Powerful events system to create games without programming
No need for coding using this system which is clear and powerful: events are composed of conditions and actions. Actions are launched when conditions are fulfilled.
This is a very friendly way of making games and is still efficient for advanced usage, contrary to most other "block"/"drag'n'drop" systems.
Pro Open source plugin SDK
The plugin SDK is open source, so if you want to extend it, you can.
Pro Lots of features to build games
The engine includes pathfinding, physics engine, multitouch support, custom hitboxes, platformer engine, tiled maps, multiple layers and cameras out of the box.
All of these features can be used without programming knowledge, using the visual editors.
Pro Quickly add behaviors to objects
Prebuilt behaviors can be added to objects. This is a very efficient way to add a physics engine or make a platformer game. Lots of behaviors are included, from the most advanced (Physics, platformer, top-down movement) to really simple one (like the behavior to destroy objects when outside the screen or the one to drag objects with mouse or touch).
And you still have full controls over your game as behaviors can be modified using the events!
Pro New documentation for gd5 is good for starting
A new doc is improving for gd5 that is nice for beginners and after that you can learn more from examples. Also, gd4 wiki is still there.
Pro Constant updates
New releases and bug fixes are consistent. New updates are released anywhere within 2 weeks or 1 month from the last one. Its auto-updater also does it job very well making life a lot easier.
Pro Online version available, compatible with iOS and Android
Thanks to its open source nature, GDevelop-App.com was built over the GDevelop engine.
GDevelop-App.com is a complete game creator similar to GDevelop, available directly in your browser and compatible with iPad and most Android tablets and phone! The app is perfect for making games directly from your sofa and you can even start a game on GDevelop-App and export it to open it inside GDevelop.
Pro Multilanguage support
GDevelop is available in many languages and even community can help in translations.
Cons

Con No collision library or other common things
Pico-8 is very minimalistic and as such doesn't come with really any abstractions whatsoever which means often you end up re-inventing the wheel.

Con Code editor leaves some things to be desired
Such as code completion and automatic indentation.

Con Costs 15$
Unlike many of the other frameworks it's not free. However this is kind of a feature because it means it's much more likely to be supported.

Con Memory restrictions could be confusing or frustrating to a beginner
Con No support for atlas/tilemap and sprite sheet
At this point, you need to separate the tileset maps or character animation sprite sheet before importing it to the engine, but the developers are working on this feature.
Con GUI is slow to load
This makes doing the simplest things, like looking at one of your maps, hard to do. In looking into this program, it can stall a PC while trying to load a sample map.
Con No 3d, not even fake 3d
This is a 100$ 2d-only game engine. You could of course use pre-rendered 3d graphics, but your games themselves will exist only in the x and y axes.
Con It's very slow
Although suggested otherwise, GDevelop doesn't compile the games - it just adds wrappers so each OS can run the HTML5 game it creates. That means it runs much, much slower than other engines that do compile games.
Con No cross-compiler
The Windows and Linux versions of GDevelop can each compile a native application; but the Windows version cannot compile for Linux, nor vice versa.
Con Optional subscription not mentioned on main site
While the engine is free and open source as stated on the main website, it does not mention that some optional features and services are actually activated through a paid subscription (two tiers: 2€ and 7€). Those features are: no nag screen shown when debugging, additional metrics available on games dashboard, access to more than 2 cloud exports per day (unlimited local export can be done without subscription, provided the right packaging tools are installed and configured), easy removal of GDevelop splash screen (can be done manually without subscription).
Con Behaviors of Objects are rather generalized
Since it has a fully GUI editor, the objects you are allowed to add in your game are pretty generalized (PhysicsObject, TiledSprite, PlatformerObject, etc). This limits the freedom of a game developer while making a game, as the object msut follow the preset behaviours imposed on it.
