The graphics are a mixed affair as far as i concern. the background is a pure proffesional graphic design/art, beatifully drawn and yet isnt interfering with the rest and actually manages to stay a background, but the heroes are bad. animation, effects and units design wise.
i got this feeling that valve's artists are frustrated that they couldnt design the units themselves, it seem like all the things that were noted as crucial for making the migration from dota easy for the players just stayed really close to the original WC3, which is really bad as the units there were kinda forced by the existing models and werent designed from the ground up to visualy match their purpose. all the other stuff were they got artistic freedom, like the catapults and the flying donkey are just great and i am sure the artists had a lot more pleasure making them than copying the models from warcraft 3.
Valve still has a lot to do before it can even compete with HoN, not to mention LoL which is really a MAJOR step up from the formula and while not yet competettively viable, is still a much better game for the non pro's (i wont say casuals, because LoL still maintain enough depth and skill requirement)