One person. General Opinion. Here you go.
1. Late light is ridiculously broken. It needs a nerf. The heal is too much and too wide.
2. Healing is too prevalent on the early units. You either build self-heal or you build Morellonomicon or Red Buff, or you will lose early.
3. Ocean sucks. It doesn't win at all. The units have very poor synergy compared to the other sets.
In terms of the Match Element bonuses, Ocean and Cloud are less strategically important than Inferno and Mountain. This is because -
* Ocean units are a dime a dozen and have poor synergy, adding Qiyana basically gives you the option to focus on Qiyana which is ok.
* Adding 30 mana to a unit at the start of the game is usually not worth the risk/complication of changing its position, the bonus is too insignificant.
* Cloud is only important if you are playing Yasuo, in which case you can run Qiyana and enable early team dodge. Otherwise it's the same as Ocean, the dodge change is not worth the risk/complication of rearranging for it.
* Inferno bonus is a major attackspeed increase, which not only builds damage but build MP charge speed and this is the kind of bonus you really want on your key unit. In addition, Inferno Qiyana is the second Inferno Assassin making it easier to sidespec into Assassin from Inferno and vice versa.
* The stacking effect from Mountain can be a crucial lynchpin for a long term unit, in particular a high rank unit with good effect that you're not confident you can get to 3-star. A lucky pull, 2-star rank 3, or carousel 4 or 5-star are all good candidates for a Mountain slot even if it puts them a bit out of position, and it rewards forethought and insight. To add one more element, Mountain Qiyana can enable super early Mountain Set Bonus, which is a very big shield. [SIC: Mountain is the Best bonus for having a Good Game]