The level of difficulty for the exams are as follows:
1. Magento Solution Specialist: This would be the easiest, as it's meant to test a person's knowledge of the features/functionality/technical requirements (including high-level questions about scaling). This is meant for Product Manager/Project Managers/Scrum Masters/Business Analysts/Quality Assurance/etc.
2. Magento Front-end certified Developer: This one is more difficult, as it requires a practical understanding of Magento's front-end and how to manipulate it. Layouts/Themes/Assets/etc are all included in this exam. You must be able to provide answers to code-level questions. Note: These questions are not general front-end web development questions, they are specific to accomplishing Magento-specific view layer manipulations.
3. Magento Certified Developer: This exam has another degree of difficulty, as it dives further into understanding Magento at a code-level. This exam will generally cover all the major functionality of Magento. You are expected to know exact: class names, exact XML node names and nesting order(s), logical flow of code/methods in various sections of the codebase. Questions will be offered which are very similar (or seem similar if you aren't working with Magento enough to clearly identify a false answer).
4. Magento Certified Developer Plus: This exam is the most difficult. This exam is the only one that includes Enterprise Edition related questions. So you must also understand the features included in M1.X EE. You will also be presented with "challenge questions," which are not identified as such. I believe that there are five in total. You can get all other questions correct, but if you miss any of the "challenge questions" you will fail.
The study guides will accurately identify what you should cover and know before taking any of these exams. They are multiple choice questions where one or many answers may be correct. The questions are designed to test a person's practical knowledge of the platform(s). It is possible to pass without really actively using the platform, but you'd have to follow the study guide closely and really dig into the product to gain this knowledge. It is best to take an exam after having spent real, hands-on time with the product. You will be notified immediately if you have passed/failed following the completion of your exam.
Note: Some may say that some of my answers are subjective due to one's area of specialty, and that's fair, but I have organized my answers in order of technical difficulty. No offense meant to anyone if there are any objections.
Passing Scores as follows:
- Magento Certified Solution Specialist exam: 39 or higher.
- Magento Certified Front End Developer exam: 44 or higher.
- Magento Certified Developer exam: 37 or higher.
- Magento Certified Developer Plus exam: For sections 11 & 12 combined a score of 7 or higher AND meet the overall passing score of 48 or higher.
I hope that this helps.