The idea was nice. The implementation is flawed. They key:chest ratio is clearly off, and it's off in the wrong direction (more chests than keys) which is quite frustrating. It feels bad to be arbitrarily gated by RNG. It would have made far more sense for keys to drop more frequently than they currently do, so that you run out of chests first. That way, better players feel good about being able to "keep up" while players who earn more keys than chests have something to strive for (mastering new champions for an S). It makes the gating feature something that is somewhat under the player's control, and gives a sense of ownership.
Instead, we have people sitting on chests unable to open them because RNJesus exponentially slows your key drops over time. It's badly designed and feels like a cash grab to get people to buy keys. Basically it feels like Riot found a new way to sell mystery chests at a higher price and make you think you like it, and it feels awful.