Dragon change in the competitive level.
I personally doesn't like the fact that changed dragon just added a huge random element into the game that can decide the outcome of the game so easily, especially in the tournament level. Remember how Riot removed Dodge, and tried to remove critical strike component (like done on ashe) to reduce the random element that can make people frustrated and unfair. Yet, this change made such effort totally in vain.
Despite all of the buffs look pretty attractive, it is only the fire dragon buff that contributes to the teamfight and character strength. In fact, a single fire dragon buff is as strong as two or three dragon buffs before. Remember the interviews what pro teams said about dragon and how they reacted to the dragon change from gold to stats. They figured out that some levels are way more stronger than others, like first dragon and fourth dragon in the first because first dragon giving stats similar to fire dragon now and fourth dragon just giving team global wide pushing advantage (and being able to clear entire wave with single skill, making losing team can't push at all). It is likely that the mountain dragon and air dragon could be just useless compared to the fire one, since I don't see the huge meta change from season 5 and am assuming the same stats would be more important than others. The improved sustain from ocean dragon is a new thing, but as most pro teams doesn't drag the fight for long and team fights are very coordinated, it is likely that the sustain wouldn't be as important as the fire dragon that can win the teamfight and the match.
I can imagine how a one pro team simply just get two fire dragon because it is just the first two that was spawned and their team comp was early game focused, while the other team with more late game comp held on well, only lost those two dragons. And yet, those two fire dragons are strong enough to just crash the late game comp with any champion comp because it is essentially giving them one more core item.
On the other hand, it is possible that the early game team just can't snowball because they didn't get the fire dragon.. Despite they secure 4 dragons in a row, non of them could be fire and it is easily doable that opponent team can fight them back once they catch up by farming. They did change the tower to lower the snowball, but it is more like determined by random element.
Hardly a good feature for an "e sport"
