I went into this movie wanting to dislike it and came away very pleasantly surprised. When watching the initial trailer, I thought I hated the animation style, but within a few minutes of starting the movie I'd already gotten past it, and by the end I'd learned to love it. As far as 3DCG films go, the quality of this one is high. The animation has a lot of respect for its characters, and there are subtle enhancements over the original that I feel a lot of people are missing. Pikachu's character is particularly enhanced by the animation style, as their movements feel a lot morerealistic, especially in the way they interact with Ash.
It's hard to complain about this movie if you liked the original, and there are very few changes made to the script, with most of them being done (in the English dub) to correct the mistakes that 4Kids made, or even poke fun (Jelly donut anyone?).
Brock feels dis-serviced by this adaptation slightly, which does upset me as he was one of the better characters, but overall this version of the film is a solid update. It wasn't really necessary, but its still fun, and still triggers the nostalgia and tugs on your heart-strings.
The voice acting is sound, especially Pikachu's during THAT scene, which is given a bit more effort his time around and hits you harder.
Overall, I'd say to give this a try even if you're skeptical, the worst that can happen is you like it slightly less than the original, which we know you already liked if you're here.