I'm a big Vin Diesel fan mainly for his Riddick character and his love of D&D. So I was really hoping this would be at least a "pretty good" film. Unfortunately, for me, instead it ended up being "just barely good."
To its credit, The Last Witch Hunter did manage to hold my interest for the full hour and 46 minutes. At the most basic level the film does have an interesting premise, characters that made me care about them--and I thought it actually featured some very good action and special effects. For that reason I won't outright pan it or recommend that you not see it.
The story itself is actually not bad for the action/fantasy/adventure genre. But the script and dialogue are too often used to awkwardly explain (literally, in an expository fashion) to the audience what is going on. It is difficult to build genuine suspense and emotional buy-in to the story when things are rushed along by having the characters continually explain what's going on to each other in order to move the plot forward.
The idea for the main character, the witch hunter Kaulder, is actually not a bad one. Kaulder was born during the European Black Plague of the 14th century. During that time period he slays a witch queen that curses him with immortality: he will be forced to outlive his mortal loved ones (i.e., so he tends to avoid attachments), and never know the peace of a heavenly afterlife. Thereafter, working with the Vatican (specifically a priest specializing in knowledge of witches referred to by the title of "dolan" in the film), Kaulder is charged with a kind of 'Men in Black' role of tracking down witches (a kind of mutant offshoot of humanity) and incarcerating them whenever they break a truce they forged with humanity long ago in which they promised to avoid affecting mortals with their magic. Kaulder must prevent the ancient witch queen that he killed from being reborn, since she will attempt to break the ancient truce by once and for all killing off all mortals. Three people help Kaulder along the way, played by Michael Caine (Dolan, the 36th), Elijah Wood (Dolan, the 37th), and Rose Leslie (Chloe, a witch "Dreamwalker"). They all do a respectable job in their respective roles, even if the lines written for them are at times clunky.
As much as I enjoy Vin Diesel, unfortunately it seems to me that he's really not working very hard as an actor these days in terms of pouring himself heart and soul into the performance itself. I thought he kind of mugged his way through this movie, coasting on his charisma. He's starting to appear transparently full of himself. As if, "Hey, I'm so massively popular with my fan base that I don't have to put any effort into this. (And I'm amused by it.)" That is not the Vin that I enjoyed in the first two films of the Riddick series, and for most of the the third film (i.e., until he gets smug in this way at the very ending of Riddick).
As mentioned, the CGI and action scenes are actually pretty good and they do keep this film afloat and moving along briskly. And there is a surprise in the story that I suppose in hindsight I might have suspected, but it did catch me unawares.
This could have been a pretty good or even very good film. More effort should have gone into making it one.