Personally, Primordia was probably my least favorite Wadjet Eye game. For one, I think it's entirely too short (3-4 hours, depending). The Blackwell games are admittedly short as well, but I think that's somewhat mitigated by the fact that it's episodic, so you can take the series as a whole. I just felt it was too much of a "go here once and never return" sort of deal, where there really isn't a whole lot of exploration. The setting is great, so I would have preferred some more areas. If it was a couple hours longer and fleshed out themes a bit, it would've been better.
I also thought that the story falls a bit flat. It raises some interesting questions about faith and choice, but I don't think that they're necessarily explored deep enough. The various endings really don't add enough variation, and are pretty lame, to be frank. Again, this is disappointing since I felt they did a good job bringing it up at least.
That said, the setting is good, and there are some gameplay refinements (auto note taking was very useful) that were great. I enjoyed most of the characters, and most of the voice acting was decent enough (Abe Goldfarb is very out of place as Crispin, in my opinion though). Overall I'd say it's average at best. I didn't hate it, but I definitely didn't love it, which was a shame, since I was really looking forward to it. Personally, if you're not in a rush to play it, I'd wait for the inevitable appearance in an Indie Royale bundle, since that way you'll likely get some other decent games as well.