fizz with flask
is
fun to play against or is he anti fun with this 
is
fun to play against or is he anti fun with this 
Flask is necessary on him to survive. If he didn't have it, it would be impossible to play him. His E is the problem. I don't think it should pop projectiles. There was a very good reason it was removed from flash.
He is kind of unfun to play against as he has the ability to outplay. Usually if he takes flask, though, means that he is weaker in lane early on then you, so you should be able to abuse him if you play aggressively. Usually when you take flask you're taking it to sustain through lane until you reach the point where you can get your first big buy, in his case it would be a sheen, so pressure him hard and hope for the best. Also if Fizz is behind(can't assassinate people) he becomes useless as an assassin who can't assassinate offers nothing except free gold for your team :D.
hes fun to play as, but not to play against