It's so easy to make a good movie (not literally, but the general recipe is pretty close to foolproof) :
Step 1 : Get a good writer, give them time to create a good story working with the source material.
Step 2 : Hire a top-shelf director and unchain them from studio nannying
Step 3 : Get a good budget and production team
Step 4 : Cast it well
Step 5 : Good movie barring some kind of disaster
Where virtually ALL VG movies end up failing is steps 1 and 2. Mediocre to horrible directors and scripts mean : mediocre to horrible movies. Great actors can't save you from a terrible director and/or terrible script.
Not a VG movie per se, but Hayden Christensen was actually quite a decent actor, and of course Natalie Portman is a superb actress. Yet they were both basically terrible in the SW prequels. Why? Terrible script and terrible director. The best SW movies had only minimal romance and weren't directed by Lucas, nor were the scripts written by Lucas. Sometimes less is more.
Look at excellent directors like Chris Nolan, David Fincher, Scorcese, etc. RARELY make even mediocre films. Now look at mediocre directors or bad directors like Zach Snyder or mr Explosions. Basically everything they make is incomprehensible noise heavy on FX and utterly lacking subtlety, nuance, or art. What bugged me especially about Zach Snyder's flashy nonsense is that BvS starred Ben Affleck, who believe it or not is actually an oustanding director. His pedigree is established now. He should have had the helm, I guarantee that it would make for a better movie than ZS pooped out.
I'd go so far as to say that if you tell me the director and their filmography, I can tell you 9 times out of 10 how a future project will turn out ahead of time. It's the single most important element at play.
The Assassin's Creed director has virtually nothing under his name, and this was probably his big break. Being somebody with no 'juice' in the industry, and helming something that I'm sure the studio suits were trying to maximize for marketing, China/International sales, and 'target demos', he probably had basically zero freedom and a ton of checkboxes to hit, along with extreme nannying from the studio. Hence : bad movie pooped out, rather predictably.
