Well I just watched the first broadcast episode that has recieved "the treatment" and I'm here to tell you that it is a GOOD thing. :-)
What they did was update all the exterior space shots, both in the opening sequence and within the episodes themselves, with the first efforts appearing in the episode "Balance of Terror" where the Enterprise meets the Romulans in battle for the first time.
As promised, the updates were done with respect for the original footage, showing updated CGI versions of the Enterprise and the Romulan Bird of Prey while appearing in shots and movements that matched the originals exactly. I've seen the episode many times, but it was VERY cool to see a clearer and more updated Enterprise along with much more detail on the Bird of Prey. Really cool little touches like the phaser shots reflecting off the bottom of the primary hull as they are fired. Also the "plasma ball" shot by the Romulan ship looked much better than it did originally.
I'm really looking forward to watching the rest of the shows as they are released, and it'll be a bit like unwrapping Christmas presents as we see the different ships and planets in each episode.
Final verdict: Thumbs up. :-)