Not having read the book or the review I can't really comment on the review, per se. But I find the complaint contradictory.
This is a D&D/D20 site. It may be a great game system but Ars Magica stuff isn't covered on EnWorld. If an Ars Magica product came out and was presented as a supplement that might be appropriate for a D&D player/DM to look at I would expect a reviewer to discuss how much was useful to D&D, how much could be changed to be useful for D&D etc.
I expect the same for setting based products (is the material useful outside of the setting, does it require a lot of assumptions that aren't present in generic settings?). Likewise if a 3.0 product came out now I would appreciate comments from a reviewer about whether it incorporated 3.5 changes and how much effort would be required to change a book to match up with 3.5.
UA seems particularly likely to get into this problem due to its peculiar marketing: on one hand it's implied that its D&D compatible, covered on EnWorld, etc. On the other hand it's really its own game system. Most UA material requires at least some work to translate to D&D. A review to D&D oriented consumers mentioning clearing mentioning that aspect of the product, and considering that aspect in giving a review rating seems more than fair.
I mean, UA could, like so many other fantasy games that are similar-to-but-different-than-D&D, not be covered on EnWorld at all.