I feel a bit uneasy about critics hailing it as "Great Art" when to me, I see it as a machine-like process of reproducing an image. It's starting to feel like a skill-based craft, similar to reproducing a nice chair, and rings "hollow" in expression. What is that artist's connection to van Gogh that inspired him to make a reproduction of "Starry Night"? Why Lego's? What does the material say about the work, and what does the work say about the man that made it... I would guess... nothing.
If the artist conceives of and creates an expressive work of art via the "pixel process," I see it as justifiable, but sometimes lacking depth... much in the way I judge Kostabi, Koons, or other non-artist-"artists." (Grabbing attention but lacking depth.) It's like the "WOW" factor is more important than the art itself.
One might say, "Well what about Chuck Close?" I have seen a retrospective of his work and he did do a lot of pixel-style work, even more pixelated than the grid portraits most people know about. (Example above is a Chuck Close Ink Stamp Drawing) I saw others done with thumbprints, blobs of paper paste, etc. But he broke down a photo without the use of a computer to tell him what tone to represent in a certain grid square.
Much of the contemporary examples though are "popped" in a computer, photo-shopped, printed out, and followed like directions for latch-hook. When you think of a drip painting , Pollock can do it 'cause he came up with it, but others who do lose out on originality. Consider Rothko's color field work, and the many who came after adding little to the genre.
Academically there is some value: color mixing, color theory in practice, and an exercise in non-traditional media that has some "wow" factor. One may argue too that it's an extension of Neo-Dada, the Pop Art of the new millennium.
I think though, without a thoughtful connection of media to message however, it's a craft item, not far removed from latch-hook or paint by numbers, and maybe that's what critics said about Warhol in the 60's.
One may argue that grid drawn portraits are the same but I'd argue the method is one we can trace back to the Renaissance, and it has been used through today by many artists in high regard. There is ample evidence that artists of the renaissance, had used a camera obscura to create images. We know some artists of that time used wire grids stretched on frames set between the subject and the artist. Though they may not have had printed photos, they certainly had close parallels.
I am not willing to toss grid drawing just yet. Though gridding is a form of reproducing an image, it must be done by hand, and the student is still in a matter, drawing from observation, though it an observation of a printed resource. Instead of doing one large complicated drawing, students create 50 or so smaller, simpler drawings.
Students are still thinking through the process, still learning to observe carefully. I try to make grid projects more "valid" by requiring students bring in images of a family member, or we take digital photos of each other, sometimes in costume, so it is "like" a commissioned work an artist of almost any time period would do.
I have not yet done a pixel-based project with my students. I just have not yet found a way to add some "meat" to the pixel "bones." If one can tie the material to the message, and further connect it to the artist making it, I could see it being more "artful." Off the top of my head, a "hunger" based theme, created with food... or an obesity these paired with candy, Homelessness images created with coins... or to make that the "point" of the project--to illustrate with pixels an image that somehow related to the pixel material... That is the only way I can wrap my head around it and justify it, it's just difficult to remain connected to the student/artist.