It's hard to say that 'The Spanish Prisoner' is the best film of the year, because it quite obviously isn't. It's more like a filmed play in that many of it's locations, especially those in the Carribean, look positively fake. What can be said, is that the film is the year's most complex and interesting film, and one of the best.
The script by acclaimed playwright David Mamet (Who also wrote 1997's The Edge) is stunning, excellent with a perfect, credible plot. It's a wonder how anyone could even come up with such a great story.
The acting is also very good. Campbell Scott, who we have never and likely never will see much of is well cast and delivers the flick's best performance. A-List star Steve Martin skips the big bucks for a good script, and it's a wonder he ended up with this project in the first place, an unlikely but excellent career move. The rest of the cast is unremarkable when put up against Scott and Martin, but still good on their own right.
If you have a liking for complicated, though-provoking puzzle-like films 'The Spanish Prisoner' is highly, highly recommended, as is the similar, more accessible 'The Game'. Very intriguing and absorbing 'The Spanish Prisoner' is a must see.