I think Telltale games did really well with the art style, they avoided going for a realistic view, the character models are all recognisable, but have exaggerated features and simplified colours and shading. It means that the game is attractive without the system demands being too high, after all this is a game available not just for the PC, but also for the wii, PS3 and iPad.
The voice cast features actors from the films including Christopher Lloyd (Doc Brown) and Claudia Wells (Jennifer) and even Michael J. Fox, though his voice is used in a cameo role. The VA for Marty McFly, AJ LoCascio, does an admirable job imitating Michael J. Fox's voice from the films. The entire cast did a great job, it has been some time since I have watched the films, but none of their performances jarred with my memories of the films.
The downside of the episodic structure that Telltale uses for these adventure games is that you can see the reuse of mechanical plot and settings. Very few environments are used only once, instead the same locations are used over and over again during the course of the series, with changes to account for time jumps and new people being in charge. Each episode opens with a fairly simple puzzle to get you going then seems to flow into a familiar structure where you have a few different puzzles that can be tackled in parallel before more plot will occur.