Outside of aftermarket parts and modification recommendations, hhkb.io aims to take a neutral view on the Happy Hacking Keyboard. After all, it's probably clear that I'm a fan - I wouldn't dedicate the time to maintaining hhkb.io otherwise!
Rather than writing reviews, here are links to high-quality coverage of HHKB models over time. I'm showing my bias here, but when considering review quality, I try to stay away from reviewers who have a hard time accepting the smaller layout and function-layer right out of the gate. A quality critical review should indicate that the reviewer is at least willing to learn the layout without making a big deal about it.
When it comes down to it, if you like it, it's good. If the idea of having to press multiple keys to send certain keycodes is an instant-no for you, then the HHKB is probably not the right choice.
Material Journal - HHKB Professional Hybrid Review
An excellent and extremely high-quality overview/review of the HHKB Professional Hybrid, with useful comparisons to the HHKB Professional 2, well-informed explanations of Topre switches, shortcomings and modification possibilities. The photographs are beautiful!
Gizmodo - This Is The Perfect Keyboard
A less-technical review by Alex Cranz. He's clearly a fan. Stay out of the comments if you want to avoid statements about the lack of keys on the Happy Hacking Keyboard layout - I'd like to think if you're here, you're past that.
A positive review that doesn't make light of the fact that the Happy Hacking Keyboard is an acquired (and not inexpensive) taste.
Seongmin Park - HHKBs compared (Pro 2 vs. Classic vs. Hybrid Type-S)
A comparison between models and not a general review, this article includes sound samples and a well-informed look at the differences between the HHKB Professional Classic, HHKB Professional Hybrid Type-S and the HHKB Professional 2.
Code and Life - HHKB Professional 2 Keyboard Review
A great review from a developer and intermediate keyboard enthusiast. Notably, Joonas discusses the learning curve involved with coming from a Finnish keyboard layout.
Leaf&Core - Happy Hacking Keyboard Professional 2 Review
Critical take by an open-minded reviewer. 60% layouts are not for everyone, after all!