Just some things I think that they're doing wrong.
Movies that are based on video games have done poorly over the years. I think the reason for this is that most of the people who make movies are unfamiliar with video games and the transition from video game to movie causes something that was in the game to be lost. The same has occurred with comic book movies. Some of them are good, but some of them are bad. The reason for this has to be how it has been adopted. If the game is normally good, then something must have happened when it was changed into the new medium. Keep in mind that while books are sometimes 1500 pages long, movie scripts can be just as long and books provide excellent source material with descriptions of what everything should look like. Poor book adaptations are usually just the result of a poor director.
It is important to remember that you cannot just convert from the original source to film. The reason is that the original source whether it be comic books or a video game is much longer and has to be condensed down into 2 hours, often less. When you attempt to do this, the story becomes rushed and characters do not get the development they need. Their change in character occurs way too fast and is simply done to just move the story along. You also need to be aware of sudden drastic changes in characters that seem off. The comic books have done this over the years and have resulted in terrible explanations for many of the behaviors of characters that seemed out of character for them.
The most important thing is the universe. Keep in mind that the world has already been established a certain way and you need to pay attention to certain consistencies. The one thing that probably should not change is the origin story. This is what causes the person to take their journey in the movie. In comic books, this is the reason for the person to become a superhero. For example, for Batman, Bruce Wayne's reason was the murder of his parents. In Green Lantern, Hal Jordan's reason was that he was entrusted by Abin Sur, but it took him a long time to embrace the identity. For Dead or Alive, the whole reason for Kasumi's involvement was to find Hayate, which causes a few of the other people to get involved. You must never forget who the main character of the story is. When you do forget, you have things like Street Fighter the Movie where Guile became the main character and everyone else just became idiots who got dragged in. Just remember Zangief's famous line "Bison is a bad guy?!?"
Video game movies have to remember this too. The first Resident Evil movie is a good example where they do their best to establish a separate continuity, but still attempted to maintain the feel of the game. It was still a survival horror. They tried to recreate the mansion death trap in another place, but also attempted to explain why in this movie. While they take their own route, they expanded it and attempted to show what was going on elsewhere during the first Resident Evil game. However, it quickly derailed into your typical action movie. This is something that you do not want to do because it immediately kills the atmosphere that existed in the game and turns it into the generic experience rather than the unique feel the game had.
It is okay to take a more liberal direction with the film and create something entirely original. However, you have to pay attention to certain background and origin stories because they explain why things are the way they are. Significant changes in those stories results in a completely different character. A good example is the recent Batman in the Flashpoint mini series. By changing the death of Bruce Wayne's parents to the death of Bruce Wayne himself, Bruce Wayne's dad became Batman and his rogues gallery completely changed. However, this resulted in a much more vengeful Batman who outright used violence and his business to keep crime under control. This is a big change, but none the less resulted from the change of one event.
The second most important thing is the pacing. Like all stories, pacing is very important. Things take time to occur and people need time to adjust to new circumstances. This could result in a change of character or reinforcing certain aspects of the character. When done right, you have proper character development. When rushed, you have people just running around for two hours and no one has time to react to what just happened. Remember that movies rarely last more than two hours, but a single comic book storyline of 5 issues is enough to make a movie that lasts 2 hours and the average video game probably lasts closer to 10 hours with RPGs easily crossing the 20 hour mark.
A good example of pacing is Batman begins. An unknown amount of time passes between major events such as the trial of the criminal that shot Bruce Wayne's parents and his training in the League of Shadows before his return to Gotham City. However, we know a lot of time has passed and according to Alfred, years passed. His change of character and experiences from his training explained how he adopted the Batman persona. At the same time, they establish a new continuity and storyline that is different from the Batman comics, yet believeable in their own world. It does revert back into an action movie, but it never loses the feel or atmosphere and successfully maintains it.
A bad example of pacing is The Last Airbender. While it attempts to adapt the entire season of a TV series into a movie, it does so unsuccessfully and the events occur so fast that you really do not feel what the characters feel. They also stripped much of the original atmosphere of the series. The pacing does not give you a sense of time and they travel across the world visiting three of the four nations of the world (2 air temples, 2 water tribes, 1 earth village). In fact, it feels like their entire journey took less than 3 days with them rushing between locations in a matter of minutes. There are some believable changes such as mastering Waterbending through the scroll that teaches all the forms and that only the strongest Fire Benders can actually create fire from their body or the air. While they tried to maintain the original feel of the series, they failed to do so due to pacing. After a supposed 100 years of the Fire Nation fighting the Avatar, after one display of power, the Fire Nation soldiers suddenly bow before the Avatar and swearing their loyalty to him despite fighting him for the last 100 years.
RPGs often lack a sense of time, which is not a very big deal. There are sometimes implications that the journey did not take more than a few days. At other times, there are implications that possibly years have passed between events. When converting that to movie form, you have to realize that you need something to show that time has in fact passed. The easiest way is through a montage, usually one for training and honing their power while showing what is going on with the rest of the world. The best way to display growth is probably through formal training of some kind implying the growth in strength of the character. A good example of a training montage is in the game Tales of Phantasia. The main characters traveled into the past to fight Dhaos where they eventually grew strong enough to push him back. However, when they return to the present, the ally they left behind was no stronger than the moment they left him. His response? Every night while the rest of the team is sleeping in the inn, he is out in the yard practicing in order to cope with the difference in strength. The result is that after all his training events, he is nearly as strong as the rest of the team. While no specific amount of time was stated, it implied a lot of time did pass and that it resulted in different rates of growth for each character.