My biggest concern would be autofocus speed. Even though many mirrorless cameras now have phase autofocus in the form of a hybrid system, they still seem a bit slower than DSLRs with dedicated phase-detect autofocus. If you're in decent light it's generally fine, but in low light and in situations where contrast is limited (smoke, fog, haze, shadowed areas) mirrorless cameras can struggle a bit. Other than that, they're light, have great sensors for the most part, and can easily be stored. Plus, lenses focal lengths/apertures are often cheaper for mirrorless systems. I'm wanting to get the Fuji XE-2 or X-Pro 2 (when it's released) just because the ease-of-use to quality factor is so incredible.