Firstly: no, it's NOT a scandal that Alan Turing isn't mentioned. He couldn't be mentioned without being made into a character and given a role in the story - which would mean, among other things, placing him on the list of suspected traitors, at least temporarily, which would either be a slur, or (assuming it wasn't a slur because we'd immediately know him to be innocent) a constraint on the mystery. Throwing in a clearly fictitious genius was the right thing to do. (Turing was the most important, but not the only, genius involved.)
The main problem with "Enigma" is that emphasis is badly misplaced. I was interested in (a) how the war effort was going, (b) whether Bletchley Park would come up with solutions in time, (c) HOW the process of breaking codes was actually carried out, and (d) when Tom would get over his idiotic infatuation with that annoying blonde chick and fall, as any sensible person would, for the dynamic and twenty-times-more-attractive Hester (Kate Winslet). I won't swear that I was interested in these things in that order, but I WAS interested in them to the exclusion of everything else; the mystery subplot involving Claire that for some reason becomes THE plot, was a distraction. Its twists and turns (they come along like clockwork every fifteen minutes) are of the kind you don't even bother trying to follow. You just wait for the next confrontation between Dougray Scott and Jeremy Northam, of which Stoppard's (or Harris's) mechanical sleight-of-hand is just a means of providing. A pity he couldn't have found some other means - or moved Northam's character to a different movie altogether, where he wouldn't take time away from Enigma, Winslet's character, etc.
The film - and the script, too, all things considered - is well put together (intelligent writing, excellent acting and photography), so the Claire subplot makes it a real missed opportunity.
