Ranked in these QuestionsQuestion Ranking
Pro Extremely easy to learn
GameMaker: Studio is incredibly easy to learn. It requires almost no programming knowledge which means that those without the technical experience, such as designers or artists, can create their projects without the help of a programmer.
Pro Gives developers access to a more fine-grained controle over the logic through the Game Maker Language
Game Maker Language (GML) is the primary scripting language that is interpreted similarly to Java's Just-In-Time compilation used in GameMaker. It is used to further enhance and control the design of a game through more conventional programming, as opposed to the drag and drop system.
Pro Easy to find resources/tutorials/assistance
GameMaker: Studio has a huge following, tons of people put up tutorial videos, and it's just generally easy to find help. It has a huge community.
Pro Easy cross-platform shader support
Write your own shaders in one shader language and have it automatically ported to all platforms. You can even choose a specific shader language to wield the full power of the target device.
Pro It has an IDE used for loading all of the assets
It is very easy to manage all the resources you want to put in your game, the UI widgets for each assets (sprites, sounds, backgrounds, rooms, objects and shaders) are intuitive enough for when adding or even editing the properties of each your assets. The included editors are also good and easy to use (sprite/image editors, shader editor and room editor).
Pro Extremely stable
GameMaker: Studio has been around since 1999 and has been used and maintained during all this time. This makes it an extremely stable game engine.
Pro Cross-platform multiplayer support
There is the possibility of creating games that interact with different platforms and is not that hard.
Pro Assets can easily be found in the official marketplace
Yoyogames website has a marketplace which opens up an opportunity for people to sell or giveaway created assets and resources (sprites, scripts, sounds, extensions, full source codes, etc.) for use in GameMaker. This benefits people who needs quality assets for their games, and for creative people to provide these assets for extra income. The Marketplace has a rating system so it can eventually increase the quality and competitiveness of the assets submitted.
GameMaker: Studio projects can be deployed to: HTML5, Linux, Windows, OS X, Windows Phone, Android, iOS and PS3/4/Vita.
Pro Easy to use
Game Maker Studios simple interface allows for rapid prototyping, and easy development.
Pro Built-in support for pixel-perfect collisions
Enabling pixel-perfect collisions on 2D sprites is so easy many will likely turn it on when maybe they might be better off without it. Regardless, it simplifies small and/or retro console-like game work. This is a feature fairly unique in this class of game engines.
Pro Supports 3D
There is also 3D support that doesn't interfere with the primary 2D focus.
Con Exporting to some formats costs extra
You need to buy extra modules to be able to export to platforms like Android, iOS, HTML5 and others.
Con The cost to buy for development is outrageous
The cost for this tool is hindering for indie developers who have little money to work with.
Con The scripting language used is quite limited
Language does not support actual objects, structs, real data types, functions, overloading, even argument naming. Developers generally have to code around the lack of these features in very tricky ways.
Con Development has been and will be cosmetic
The change from 1.x to 2.x was cosmetic, the engine and language stayed the same. The roadmap for future development is also cosmetic and includes updating the sprite editor, adding an audio editor, and adding a "mini map" for the IDE.
Con No built-in refactoring tools
There are no built-in refactoring tools. For example, you can rename a resource, but GM:S will not automatically change the mentions of it across the code to the new name. Furthermore, because all file formats are text-based, basic refactoring could be achieved by simply doing "find & replace in all files" -- which is a feature offered by pretty much every external code editor nowadays -- but no such feature here. Hitting Ctrl-F will pull up a rather odd Find/Replace box but selecting a word before hitting Ctrl-F will not autofill the Find field for you like it will in most tools. Even that you have to cut and paste yourself.
Con Destructive DRM
In late 2012/early 2013, YoYo Games released a version of their new Studio IDE for cross-platform development that would import games and destroy all of the image type resources for some legitimate purchasers of the software by superimposing a pirate symbol on top of the image. This was due to a fault in their digital rights management software implementation which they use as a method of combating pirated copies of the software. Though the false positives bug is reported to be fixed, the DRM is still in place and may affect placeholder graphics, etc. YoYoGames publicly stated they would remove the DRM at a later point in time, but that other less-invasive DRM techniques would remain.
Con Can't embed videos in game
Doesn't support embedding videos in a game.
Con Bad history of ignoring critical bugs
In the past, the developer failed to update the software for iOS and Android when game-breaking updates were made to those platforms.
Con Expensive for what it offers
There are several options with more flexibility, better learning resources, and a lower price point.
Con Poor level editor
No marquee select, no layers, can be glitchy, no grouping, etc.
Con Proprietary language forces expensive "lock in"
Because it uses GML, a very non-standard custom language, new users do not learn a transferrable language and become locked in.
Con Tends to crash or not compile games properly
Con No GUI editor
The GUI must be hard-coded, leaving a lot of tricky calculations and jumping through hoops to accommodate different devices and displays; it's probably the least developed and hardest thing about GMS2 compared to comparable engines
Con Poor accessibility and integration
Documentation and resources largely focus on proprietary scripting language, which is necessary for achieving full potential of the software due to poor drag and drop integration.
Con Code editor not friendly to indented code
While the editor of course has features for intending code such as auto indent and smart tabs that can be turned on or off, these features work in unusual ways and, overall, the editor is not very adaptable to various typing styles. Also, Home always takes you to position 0 and never to the beginning of the text no matter how many times you hit it. Thus, if you hit Home and then Enter a new line, with auto indent on, it will always mess up the indentation on the line following the new line leaving you to fudge around to fix it manually. If you prefer tabs over spaces, forget it. Finally, if you leave the GameMaker app and try to click back into the code editor, the code editor will not fully get the focus sometimes leaving you with the ability to type but not tab. It usually takes two clicks to fully focus the code editor from outside the GM app.
Con No way to activate or use existing modules
Support entirely focused on new iteration depriving even basic functionality of this version with any purchase that hasn't already been activated. It is still possible, thought not intuitive, to download this version on the trail screen for GM S 2. But no purchased (wildly expensive) module can be added any longer.
Con This is very flat for games
They are not beautiful - for example, Undertale.
Con Owned by a gambling company, Playtech
As opposed to other engines, which are open source or owned by game companies, GameMaker is developed by YoYoGames, which is owned by Playtech, a gambling software company.