Jeff Bond's review of "The Ultimate Computer" at Trekmovie.com contains one of the most cogent and accurate summaries of the successes and failures of this whole project:
Looking at the whole Remastered Project
I certainly agree that the digital mattes were the consistent high points of the new versions. And what he says about the spaceship CG is true of the least successful examples:
It’s a trade of one type of unconvincing approach (heavy matte lines and film grain being the chief vice of TOS) for another in some cases.
Add "notable compositing failures" to the "heavy matte lines" complaint.