and it appears that he tries to avoid being overly critical.
He's not always so nice, just depends on which reviews you look at:
Sigma 20mm f/1.8
"Unfortunately, I consider the Sigma 20mm f/1.8 EX DG Lens to be unusable at f/1.8 unless you are looking for a soft-focus effect. This lens is one of the softest I've seen wide open.
In conclusion, I recommend not buying the Sigma 20mm f/1.8 EX DG Lens. Sorry Sigma, this one is a dud."
It's not just sigma:
"The Canon EF 80-200mm f/4.5-5.6 II Lens is a very small, very light and very cheap telephoto zoom lens.
There is no sticker shock when checking the price on this lens. But, as often is the case, you get what you pay for.
With the Canon EF 80-200mm f/4.5-5.6 II Lens, you also get very cheap build quality.
Optically, the Canon EF 80-200mm f/4.5-5.6 II Lens is disappointing.
Basically, the Canon EF 80-200mm f/4.5-5.6 II Lens is a very cheap telephoto zoom lens with performance relative to its cost."
Sure, with the L lenses and 1-series bodies he's not going to be too negative, but even in the 1DX review he says things like:
"...but first, I want to point out a potential downside for 1D Mark IV body owners looking to upgrade to the 1D X... This is of course disappointing to many extender users... The largest group of photographers affected by this change are, probably, bird photographers (such as Arthur Morris) - who have been dealt a double blow with the 1D X. Bird photography typically needs the most reach possible - through both lens focal length and sensor density. Increasing focal length via extenders has now been limited (for autofocus to function) and the 1D X has a less-dense sensor than either of the previous 1-Series models...
This is, perhaps, the end of that era. I have to admit that I'm surprised by this design decision. "
He sounds almost British here, being polite as possible about a change for the worse when you can really tell he's annoyed by the no f/8 and knows a lot of others are too.
You just have to read between the lines a bit when reading his reviews, to tell which lenses/bodies he loves and which ones not so much...
I like his reviews, and his site, and his lens comparison tool is fantastic (and unique I think!) so don't get me wrong here. I am a fan. So don't take the following as criticism of his character or the value of his reviews, or the effort he puts in.
But saying he trashed a Sigma lens and sniffed at a few hapless non-L Canon lenses is missing the point. My one niggle with Bryan's reviews is that sometimes it feels like he's never met a red-ring lens he didn't love (unless it has just been replaced with a new more expensive red-ringed mk2 lens), and he never gives the same kind of unqualified praise to any 3rd-party lenses.
I don't call it a "bias" because that word has negative connotations, and he does it with great intentions. I just think it is a point-of-view he brings to it.