The main criticism of _Vienna, Marzen, Octoberfest_ (VMO) by G. and L. Fix is that the contained recipes use pilsener malt enhanced with caramel malt additions rather than "authentic" vienna malt. I do not agree with this criticism.
The Fixs' reason for this approach is clearly explained: quality vienna malts were hard to come by at the time of writing, and in light of this supply problem, an alternative formulation was necessary. Continental pilsener malt is closer to vienna malt than standard american 2-row malts, and so it was the natural pick. Contemporary brewers have reasonable access to higher-quality European vienna-style malts and may be able to formulate more authentic recipes, though it is still the case that darker colored malts tend to be made from lower grades of barley. Even though the homebrewer has access to authentic vienna malts, he may still prefer to follow the Fixs' lead in the likely scenario that the vienna-style malts he has access to are not especially fresh; since Pils malt often has a better turnover than specialty styles, it is likely to be fresher. A formulation using crystal malt will also not display as much harsh graininess. While long lagering will generally compensate for such problems and may reward the brewer with a finer product, many home brewers do not have the patience or space to lager a batch of beer for several months, which makes the Fixs' alternative formulations more attractive.
A hybrid of the Fix's approach with the "purist" approach is vindicated in In _Brewing Classic Styles_, Zainasheff and Palmer recommend around equal parts continental pilsener, vienna, and munich malts for both Vienna and Oktoberfest beers (the latter containing caramel malt as well). In addition, Daniels writes in _Designing Great Beers_ that one can be successful in brewing Vienna and Oktoberfest styles using "Munich, Pilsener, and Vienna malts in virtually any proportion (337)."
In addition, while no explicit recipe is given, VMO does present historical information on the vienna style that any experienced brewer could use to formulate an "authentic" or "throwback" recipe. Here's a start: use exclusively vienna-style malt; target between 1.055-1.060 original gravity; use a decoction mash procedure to develop further color and flavor; use styrian goldings or similar hops for all additions, targeting about 30 IBU (perhaps higher to compensate for loss of bitterness over the long lagering time); split the wort and ferment with two different yeasts: one fruity lager strain and one clean lager strain (or even one fruity ale strain and one clean lager strain); blend the two beers before lagering for a heck of a long time.
Another reviewer pointed to Richman's book on Bock beers as an alternative to VMO. I do not agree that _Bock_ is a better alternative, but Richman's book is a great resource for anyone interested in perfecting older lager brewing techniques like decoction mashing---essential for anyone interested in producing turn-of-the-last-century-type lager beers including throwback versions of Vienna and Oktoberfest.
VMO is definitely not the strongest book in the classic beer style series, but the criticism I have seen in reviews on this website is overly harsh.