Many reviewers were caught with their pants down. But in their defense, they're used to reviewing 2-hour movies. They don't have time to review all 26 episodes because they want their review out ASAP for page views.
Some admitted to basing their review off the sampler disc for Encounter at Farpoint assuming it was exactly the same (not a bad assumption), and then cherry-picking some of the episodes which just happened to be unaffected by the audio glitches. One even noted "tinny" audio for Haven, but brushed it off.
These same reviewers (Blu-ray.com, highdefdigest) are likely just popping in TNG this time around to look at grain structure, the audio mix (so they don't get burned a second time) and probably the color. Few, if any, know about HTV or the lower quality visual effects. It's up to the fans to let the reviewers know something is wrong.
I forwarded some of the worst screenshots (including the compositing error) to Bill Hunt at The Digital Bits. We'll see if anything comes of that. Thankfully, Trek fans are loud.