With its SLT series of cameras, Sony spans a gap between mirrorless Interchangeable Lens Cameras (ILCs) like the Olympus PEN series, Panasonic's Lumix G series, and Sony's NEX models and Samsung's NX series and traditional dSLRs. The defining difference between the two categories is a mirror: in ILCs, light travels directly through the lens to the sensor, while in dSLRs, the light is either reflected up into the viewfinder by a mirror or allowed to directly hit the sensor for capture if the mirror is flipped up. The SLTs have a fixed, translucent mirror--hence it lacks the "reflex" of an SLR--which splits the light path.
Also known as a pellicle mirror, a TM passes most of the light from the lens through a fixed semitransparent mirror, reflecting a small bit of the light upward to a separate phase-detection autofocus sensor. This is how Sony achieves the faster phase-detect continuous AF for movie capture, while most current ILCs and dSLRs use the slower contrast AF, which is based off the imaging sensor. It also means that the camera can achieve the faster still-photo autofocus speeds associated with dSLRs.
One doesn't necessarily need to use a mirror to incorporate phase detection, though; for example, Fujifilm's recent F300EXR point-and-shoot uses a phase-detection array layered over the image sensor. Because many older dSLR-mount lenses can only work with phase-detection AF--that's why ILC adapters for older lenses generally don't support AF--Sony's system enables autofocus when using those lenses for shooting video.
The trade-off is in the viewfinder, however. Unlike a dSLR, but like some ILCs, the SLT uses an electronic viewfinder. That's because the amount of light reflected up to the phase-detection sensor isn't enough to sufficiently illuminate a dSLR-like optical viewfinder. So the shooting experience of the SLT-A55V is a kind of hodgepodge as well. And because the mirror doesn't perform the single most important function it serves in a dSLR--enabling an optical viewfinder--we categorize the SLTs as ILCs rather than as dSLRs as Sony's marketing does.
I have mixed thoughts about the A55V's photo quality. By many objective standards it fares pretty well for its price class. In JPEGs up through ISO 1,600 it does a decent job balancing noise and detail. At ISO 3,200 photos look acceptable unless you've got a lot of fine detail or edges where softness will be too obvious. I find you can get sharper results with more attractive grain by processing the raw files, but the trade-off is more clipping in the shadows; there doesn't seem to be a lot of dynamic range to play with. For high ISO sensitivities, Sony has vastly improved its noise-reduction feature in recent cameras. While there are still some obvious artifacts, there's a much better balance between sharpness and color noise reduction than I'm used to seeing in photos shot with older models. And I was pleasantly surprised by the quality of the noise reduction at the camera's highest ISO 12,800 sensitivity--"pleasantly surprised" doesn't mean it's more than an emergency mode, as with its competitors, though.
Furthermore, though it lacks a neutral color setting, the standard Creative Style parameters didn't induce too much of a color shift, and it delivered very good color accuracy numbers in CNET Labs tests--better than most of its low-end dSLR siblings. Nor does the camera seem to oversharpen, either. But none of my photos really wowed me, and I shot about 500. Most had a very point-and-shoot quality to them--not the oversharpened look, but the details-never-really-resolved appearance, even with expensive lenses--and there's an overly cool white balance in daylight.
For point-and-shoot upgraders who want better video, the A55V gets a qualified recommendation; the quality is pretty solid, it can autofocus well enough for casual use (albeit loudly--you'll definitely want to use a hot-shoe microphone), and the interchangeable-lens system means you'll be able to put on a long zoom lens for shooting your kids' sports or school plays. Much has been made about the SLTs automatically shutting down for overheating--and it happened to me on a particularly hot day--but keep in mind that no dSLR or ILC can shoot for long stretches without needing a break (here's Sony's table of estimated durations). They're not camcorders. Using the image stabilization really cuts into the recording time, though.