1. Introduction of the game:
Embark on a futuristic journey into the world of high-octane robot boxing with Real Steel, a game inspired by the 2011 film featuring giant mechanical gladiators. This fighting game combines intense action, strategic gameplay, and a rich storyline to bring the excitement of robot combat to your fingertips. With its immersive environments and cutting-edge graphics, Real Steel allows players to experience the thrill of the sport as they build, customize, and battle their way to the championship.

2. All characters and levels of the game:
Real Steel hosts a diverse roster of characters, each with unique abilities and design, echoing the robots from the Hollywood movie and expanding with original creations. Players can choose from fan favorites like Atom, Zeus, Midas, and Noisy Boy, among others. Each character brings its own fighting style and special moves to the ring. As for levels, the game features a variety of arenas that replicate the cinematic feel, offering multiple tiers and challenges to test your mettle as a robot boxing champion.

3. What attracts users most to the game:
Players are most attracted to Real Steel's intense combat mechanics, the ability to upgrade and customize their robots, and the authentic representation of the movie's universe. The interactive environments, responsive controls, and competitive multiplayer modes also keep players engaged, offering a fulfilling sense of progression as they rise through the ranks.

4. Why it is popular:
Real Steel's popularity can be attributed to its loyal fan base from the movie, as well as its exciting gameplay that appeals to both casual gamers and hardcore fighting enthusiasts. The game has managed to capture the essence of robot boxing and provide an accessible platform for strategic fighting, making it a hit among audiences looking for both entertainment and depth in their gaming experience.

5. When the game was released and how many versions are currently available:
The Real Steel game was released in conjunction with the film's debut back in 2011. Since its launch, the game has seen several updates and versions, including Real Steel World Robot Boxing and Real Steel Champions, each adding new elements, characters, and features to enhance the overall experience. The exact number of versions can vary as the developer continues to update and expand the game.

6. The most difficult part of the game:
The most challenging aspect of Real Steel lies in mastering the robots' different fighting styles and adapting to high-level AI opponents that require strategic thinking and quick reflexes. Additionally, the multiplayer component can be particularly tough, as it pits players against real-world opponents who may have superior robots and skills.

7. Strengths and weaknesses of the game:
Strengths of Real Steel include its engaging combat system, the wide range of customization options, and its faithful representation of the movie's universe. Its weaknesses might include occasional repetitiveness in gameplay and the potential for in-app purchases to provide an advantage, potentially impacting the balance of competition.

8. What other games have been developed by the same developer:
The developer behind the Real Steel game, Reliance Big Entertainment, has worked on several other titles across various genres. They are known for developing games like Pacific Rim, WWE Mayhem, and Ultimate Robot Fighting, each of which emphasizes action-packed gameplay and immersive worlds, staying true to the cinematic properties they are based on.