1. Introduction of the Game:
8 Ball Pool is an engrossing online multiplayer pool game that simulates the real-life game of 8 ball pool, also known as solids and stripes. Developed by Miniclip, this virtual rendition allows players to compete against each other from across the globe in turn-based matches to test their precision, strategy, and cue control. Embracing simple mechanics but boasting deep strategic play, 8 Ball Pool is a virtual cue sports adventure accessible on various platforms.

2. All Characters and Levels of the Game:
The game doesn't involve characters in the traditional gaming sense, as players represent themselves or their customized avatars. As for levels, players progress through ranks, starting as beginners and advancing through levels named after real-world pool terms and venues. Progression is marked by gaining experience points, which unlock higher-tier matches in more exclusive locations with higher stakes.

3. What Attracts Users Most to the Game:
Users are most attracted to 8 Ball Pool's competitive gameplay, which remains easy to learn but challenging to master. The game's social aspect, including the ability to play with friends or against random opponents, adds a layer of enjoyment and engagement. Other attractive features include regular tournaments, the ability to collect and use various cues with different attributes, and the game's rewarding progression system.

4. Why It Is Popular:
8 Ball Pool's popularity can be attributed to its accessibility and its near-universal appeal – pool is a game that many are familiar with and enjoy in real life. It translates perfectly to the digital platform, retaining the skill and strategy while removing the barriers to entry. Additionally, its cross-platform capabilities allowing for a large and active player base, and frequent updates with new content, keep the game fresh and engaging.

5. The Most Difficult Part of the Game:
Many players find advanced competition to be the most challenging aspect of 8 Ball Pool, particularly in high-stakes matches against seasoned players. Precision shots, bank shots, and understanding complex cue ball spins (English) represent the game’s steep learning curve which requires practice and skill to master.

6. Strengths and Weaknesses of the Game:
8 Ball Pool's strengths include its addicting gameplay, robust community, regular updates and events, and seamless cross-platform integration. However, the game's reliance on in-app purchases to fully experience all features, potential network instability, and occasional perceived matchmaking imbalances can be considered as weaknesses.

7. What Other Games have been Developed by the Same Developer:
Miniclip, the developer behind 8 Ball Pool, is renowned for a variety of popular online games. Some notable titles include 'Agar.io', 'Soccer Stars', 'Bowmasters', 'Mini Militia - Doodle Army 2', and 'Plague Inc.', among others. These games span different genres, showcasing Miniclip's diversity in gaming development.