Soooo....to summarize and eliminate several paragraphs of text, Zero Punctuation is entertaining and interesting, but somewhat hyperbolic in its criticisms and probably not used as a sole source of data for the actual contents of a game. I'm not sure if you intend to write for a living or not, but if so, brevity is an important creature to get across.
That said, you're setting up a rather narrow definition for what constitutes a valid review. As a total evaluation of a consumer product, I'd tend to agree that Zero Punctuation doesn't do a very good job, mostly because I think any person would have a hard time hitting all the finer points of a game's design, presentation, and technical implementation in five minutes without boring us all directly to death. However, if you open up your criteria for what constitutes "valid" criticism to include the sort of point-by-point analysis that strikes on all of these tiny, niggling flaws, Zero Punctuation does its job well. More importantly, you should understand that this is how at least one person actually experiences the world - I live this pretty much all the time. Part of it is conditioning from my job (I build software, which requires a degree of hyper-criticality to catch all of those pesky outlying test conditions that users do so love to leap directly into and break your marvelous tool) and part from whatever interesting mental disorder I have that makes me the way I am, but when I experience ANYTHING I mostly perceive the flaws. I can say with certainty that it hasn't stopped me from playing video games in general yet, and there hasn't been a single one that I've played to date that I haven't had a list of complaints about. You can still love something and rip on its every tiniest detail and failing - it's just different from the way that most people do their thing.
All that said, regarding Zero Punctuation as being somehow less valid because Mr. Croshaw has to tailor his reviews to be entertaining would be a grave error. Aside from the occasional factual error (or, more commonly, exaggeration - for instance, I don't understand how a human person with working eyes could confuse some of the environments in Oblivion with some of the other environments in Oblivion, as was implied in his review of that game, and there have been other issues cited in the past where rare bugs were exaggerated for the sake of entertainment), all the points that Yahtzee makes are valid, relevant, and important, and hey - somebody has to notice this crap, unless of course you want to suffer through the same annoyances in your games tomorrow that you do in your games today.