The problem I have with movies based off of computer games / video games / board games is that they are often horribly made, have bad plots, often missed the point of the game or story, and/or had very little staying power - as in you watch it one time and then if you ever watch it again you become disappointed with it the second time and never watch it ever again.
Battleship - great board game, awesome movie. I have totally watched that movie multiple times.
Conan the Barbarian - The new one is based off the computer game, not the original Robert E. Howard books. I felt the movie is good the first time you see it, but really boring the second time you see it. In retrospect I now consider that movie to be horrible. For multiple reasons, each of which are due to meddling by the video game company Paradox Entertainment.
Dungeons and Dragons - Awesome roleplaying game, horrible movie during which the plot made very little sense, the villains were ridiculous, and it was amazingly cheesy.
Dragonlance: Dragons of Autumn Twilight - Awesome book / roleplaying game series, but the movie was horribly animated. Done properly, the Dragonlance series could be an amazing series of films - but you would need someone like Peter Jackson to do it justice, and it should be live action, not animated.
Wreck It Ralph - Technically there was never an arcade game with this name, but it was still a pretty good animated movie.
Pixels - No comment. I have not seen it yet.
Review of Warcraft - Four stars out of Five. Not a great movie (like Avatar), but not horribly bad.
The film has an underlying environmental theme, which I feel could have been elaborated more on.
Also the film left it open for sequels, which makes the fans happy. However I should point out that the "artsy fartsy movie critics" will not like this movie, as it doesn't offer much in the way of substance. Fans of warcraft will enjoy it, and myself, someone who is not a Warcraft fan but I am a fan of the fantasy genre, I enjoyed. But it wasn't a "great movie".
But it was good. It is worth watching. But it won't make the artsy fartsy critics happy, but to be fair those same critics thought "LOTR: Return of the King" was a bad movie. Depending on which "reviews" you read people are either saying that Warcraft financially tanked (which is false), or that Warcraft broke records. The latter is true. It is now one of the top 3 most grossing movies based on video games. The mixed responses tell me that some movie critics want the movie to fail and are apparently spreading false rumours about the film tanking. Anyone who can do math will realize the film was extremely popular.
I also feel the burgeoning love story of two main characters could have been explored more. Clearly that is meant to entice us towards sequels, which look likely as the film has already doubled its money - and the director is already talking about prepping for a sequel.