As far as the player himself goes, I don't see any major red flags. This isn't a Sancho-type situation. That said, opinions from Porto fans are all over the place, so it's clearly too early to make a real judgment. That being said, the team's handsomeness index just took another hit. The guy looks like a hangover French fisherman.
It's a shame we never got to see Costa given a proper shot. I know I'm in the minority for rating some of his qualities, but he had that je ne sais quoi. Only time will tell.