The car in these photos is heavily camouflaged, with the requisite wrap and black plastic cladding all along the body. While it may be hard to make out details, look for styling similar to that of the Ford Fiesta we recently saw. That means an evolution of the current style, with sharper, cleaner lines all around.
Both the front and rear appear to be more blunt and upright than the current model. The windows are slightly different and don't go back as far. While the lights on the front are obscured, we can see that the taillights appear to flow into the tailgate. Aside from that, it's hard to say what's changed.
Since Ford hasn't officially announced a new Focus, we can only speculate as to what will power it. Rumors suggest that the new model will ditch naturally aspirated engines in favor of an all turbocharged lineup. Ford already considers its EcoBoost the flagship engine line, so this wouldn't be that much of a surprise. The Focus appears to be on the early side of development, so expect more spy photos leading up to the full reveal.