If there's one thing that I respect about anime that's been adapted from any sort of visual novel/dating sim/choose-your-own-adventure type deal, it's the fact that more often than not, they have to try to take key plot elements from all the routes of said novel or sim, and meld them all into one single often-times chronological beginning-to-end storyline. A number of series out there do this remarkably well. Anyone who's watched the Clannad and Kanon anime AND played the games will note how accurately the backgrounds of each of the characters were portrayed, usually with no particular character's backstory standing out more than another. Of course these two are not the only series out there that attempt this feat; other series use the same concept with varying degrees of success. Where does Fate/stay night fall?
As a recap for those who have yet to see the anime or play the visual novel, the story of Fate/stay night revolves around a fictional phenomenon in Fuyuki City, where the story takes place. This phenomenon, known as the Holy Grail War, takes place every couple of decades, and is essentially a big ritual between 7 mages in their attempt to claim the Grail as their own. Each mage is allowed the assistance of a single magical entity known as Servants, powerful spirits and familiars whose souls are drawn from great heroes from history, legend, folklore, and myth. These 7 factions fight it out with each other until one is left, at which point the Holy Grail will grant the victor one wish. This, I think most people would agree, is as intriguing a plot concept as any.
At this point, however, it's incredibly difficult for me to rate the series as unbiased as I should be, and there's also the question of whether or not the visual novel should make a difference, as I should be rating the series in terms of its ability to stand alone. However, I think the factors mentioned above are still not completely irrelevant. Take this into consideration; the three routes in the visual novel Fate/stay night are incredibly different in terms of plot. Different characters live and die in each one, details about certain characters are presented differently or not at all, Shirou is less annoying in certain routes than others (waiting for Unlimited Blade Works, anyone?); this is all the more important in context of Fate/stay night's central story. Had the anime chose to simply portray one route, certain details would have been omitted and resulted in a lot questions left over by the anime's end. In this regard, I respect the effort by the creators of the anime in attempting to address all the inconsistencies that come with trying to merge the important elements of all three routes into one anime series, something which I believe they did a pretty decent job of. The anime is still mostly based on Saber's route, Fate, but with the addition of more details introduced through added events. This creates a few minor inconsistencies, but these are usually easily forgiven by viewers who are familiar with the original story.
Unfortunately, this is where the hurdle is. Inconsistencies that seem minor to Type-Moon fanboys and viewers who have played the game will throw other viewers for a complete loop. Even I have to admit that the way certain characters were introduced later in the series made those characters seem like random additions, while in reality the viewer would most likely have already encountered that character early in the visual novel. Additionally, certain details that are emphasized in the visual novel are left out for the sake of time in the anime. Character personalities are mostly accurate, but as I mentioned before, the backgrounds of various characters are presented in a simplified fashion, or not at all. Again, taking Shirou as an example, I think most people would agree that the anime portrays him as a somewhat stupid/stubborn/annoying/foolish male lead. Sadly, that's not the only side of Shirou there is, but that's mostly what the viewers of just the anime will see. This coupled with the acknowledgement that even the visual novel itself had its fair share of weak points makes me understand where the opinions of casual viewers may be coming from.
In the end, Fate/stay night the anime series suffers its share of pitfalls that are inevitable in this kind of adaptation. While the plot concept is strong, and the storyline execution is mostly good, certain discrepancies simply can't be ignored, especially considering that most people who will end up watching this will not be Type-Moon fanboys, and will not be as forgiving. Even so, I can't bring myself to give the series a rating of any less than 7. This isn't just because I'm a Type-Moon fanboy (I absolutely love all their works. Check out Lunar Legend Tsukihime and Kara no Kyoukai), but because Fate/stay night was the one anime that I watched on a whim, and completely changed my standards of anime from what it had been, and looking back now, my standards back then were pretty scary truth be told. So... take my rating with a grain of salt. I definitely enjoyed the series and believe that it's of good quality, but if you're just a casual viewer or if you're not tolerant of minor inconsistencies in the plot, just know that your opinion may differ greatly from mine.