1. Introduction of the game:
Cover Strike CS is an exhilarating mobile first-person shooter game that transports players into a world of tactical combat and strategic warfare. It's designed to give players an immersive experience of close-quarters combat bringing together fast-paced action with a strategic edge. Players must navigate through intense battlefields, utilize cover effectively, and execute precise shots to survive and complete their missions.

2. All characters and levels of the game:
Cover Strike CS boasts a diverse roster of characters, each with unique abilities, strengths, and backgrounds that cater to different playstyles. These characters range from elite marksmen to explosive experts, allowing players to choose their preferred combat approach. The game features multiple levels characterized by varying environments—from urban landscapes to deserted warzones—ensuring a fresh challenge at every stage and requiring adaptable tactics to progress.

3. What attracts users most to the game:
Users are mainly attracted to Cover Strike CS due to its high-quality 3D graphics, realistic physics, and a wide array of weaponry that captures the feel of a true conflict zone. The intuitive controls and satisfying feedback from successful hits make the gameplay experience deeply engaging. Additionally, the game's multiplayer component allows for competitive play against others, heightening the thrill of the game.

4. Why it is popular:
Cover Strike CS is popular because it successfully combines accessibility and depth. The game is easy to pick up for casual players, yet it requires skill and strategic thinking to master, appealing to hardcore gamers as well. The developers have managed to balance the simplicity of mobile play with the sophistication expected from the FPS genre, leading to broad appeal.

5. When the game was released and how many versions are currently available:
Cover Strike CS was released on [Insert Release Date], and since its initial launch, the game has undergone several updates and expansions. As of my knowledge cutoff in 2023, there are [Insert number of versions] versions available, each bringing new content, improved mechanics, and refinements to the overall gameplay.

6. The most difficult part of the game:
The most challenging aspect of Cover Strike CS tends to be the higher levels, where the AI opponents are programmed to be highly reactive and tactical. Additionally, multiplayer matchups can be quite difficult, as they pit players against human opponents who may have superior strategies or more experience.

7. Strengths and weaknesses of the game:
Strengths of Cover Strike CS include its gripping gameplay, diverse character pool, and meticulous attention to detail in weapon and level design. However, the game is not without its weaknesses, such as occasional balance issues between characters and limited game modes, which could be expanded to offer more variety.