Disclaimer: Writing this review qualifies me for entry into a drawing by lenshero.com. That said, the opinions in this review are honest and mine alone.
In the last few years I've developed a strong interest in photography, and as such I've been trying to build up my lens arsenal (in addition to a nice camera body and accessories). Good lenses often cost more than the cameras themselves and contribute more to the quality of the final product than any other component. Despite that, I have been frustrated by the lack of comprehensive lens review sites. When I'm in the market for a particular new lens I have a lot of options, from the camera-brand (Nikon/Canon) lenses to third party lenses, with each brand offering various options at different prices. It's difficult to tell what the best buy is when you're comparing lenses with different specs, and often you can only find a particular lens reviewed at one or two sites, while the lenses you want to compare it to are reviewed on one or two different sites.
In this regard lenshero is very valuable. It has a huge database of lenses. Unlike other sites where you might find just a few lenses for each category, lenshero seems to have just about any lens you can think of (or at least all the ones I've looked for so far). They also have a great interface for finding a list of lenses to fit your requirements. You start your search by selecting a camera (so that you only see lenses which fit your camera), a price range (really just a maximum price), and a general lens type. If you're new to photography then you don't have to worry about knowing what to choose at this point; the categories are described in terms of the kind of picture you want to take (portrait, wildlife, sports, landscape, macro, etc.). If you want to skip ahead to something more specific you can just scroll down and choose one of the many categories linked on the main page.
Once you do your initial search you then have a list of compatible lenses. At this point you can really start narrowing down your options by adding requirements like maximum aperture, maximum focal length (for telephoto) or minimum focal length (for wide angle), image stabilization options, brand, etc. This is the most useful part of the site. When you first start thinking about buying a lens you have a huge number of options. This interface (which is very easy to use) helps you quickly narrow down your options based on what matters most to you.
Once you have narrowed down your search to a few lenses you can start to compare them. Clicking on a lens gives you a listing showing reviews and ratings (from B&H Photo), a list of pros and cons, and a nifty table of tech specs that shows how each spec compares to similar lenses. All of this information is very useful and well organized.
Unfortunately, the site doesn't have everything I would hope for in a lens review site. Specifically it lacks real numbers on important qualities like resolution, vignetting, barrel distortion, chromatic aberrations, and so on. When it really comes down to it these are the numbers that matter the most, and they can really only be based on actual testing of a lens (not a listing of marketing material). A long lens is less useful if the images at the long focal lengths are too soft, but lenshero just doesn't have that data available. This means that you will still have to go to another site to compare those specs.
Speaking of comparisons, I couldn't find out how to take two or more lenses and directly compare them within the site (other than opening each one in a tab and comparing myself). It would be nice if there was a way to select some lenses and view a table comparing their various specs to each other on one page.
Lastly, one of the biggest drawbacks to the site is that the reviews are not made by professionals. They are drawn from customer reviews on B&H Photo, and at least one review I looked at specifically said it was written by an "amateur". It's nice to know that an amateur loves this lens, but I'd like to know what a professional thinks. That's not to say that I'm a professional, but I would trust the opinion of a professional over some random person (myself included) saying he thought the pictures looked great. This also comes back to the need for real, quantitative data instead of relying on subjective reviews.
Overall the site is a welcome addition to the few lens review sites available. Despite the drawbacks listed above, it's still a great way to at least start your search for a new lens, and if you're looking for something cheap then it may even be your only step. If you care a lot about quality, though, then it's only a first step, and you'll still need to rely on some other sites for more data to make a good decision. I like sites like photozone.de and dpreview.com for those kinds of reviews (sadly, they rarely overlap, so comparing lenses directly can be challenging still).