The ZS40's viewfinder is a feature not often seen on cameras of this size, and for good reason -- Pocket-Lint calls its presence "mis-matched." Putting that aside, in day-to-day usage the ZS40 is simple enough, and Digital Versus finds it's "easy to get the hang of everything." And while the photo quality may not blow you away, it's not disappointing either, and Photography Blog says it offers "great image quality for this type of camera." The video quality is about the same, with Expert Reviews saying details aren't "razor-sharp" but still look "smooth and natural."
With a sub-$500 MSRP there are definitely trade-offs, but the ZS40 offers enough to be put in a pocket and taken along on your adventures. If you need something with just a bit more oomph, consider Canon's PowerShot S120 instead, a solid option that offers great image and video quality.