I did not play this event on Beta, but halfway through it on Live, enough to give my personal feedback.
First, some minor things:
I do like the zodiac sky artwork! I did like the mermaid chests (shells) better than the zodiac chests (spheres), simply because they had more different looks and thus were easier to recognize and pick.
I do like the "rotate to shuffle" of the chests after you click on one. At least the beauty of it. But not the time involved. It seems to me that each shuffle takes less time compared to mermaids, but still, while clicking through some thousand keys, the shuffle time will add up and eat a complete evening of my spare time. I would love to be able to see and click the next chests without waiting for the visual shuffling effect to be complete.
I do like the different chests, which allow me to choose between higher chances for daily prizes, for main prizes, or chest rewards.
I do like the main prizes being given as early quest rewards and getting evolution artifacts by gambling. Last year at Harvest Festival, it was sheer luck whether we would get Krarak or not. I won on one server but lost out on the other two; felt like a hit in the face after completing all quests. With artifacts, luck decides between getting your building to level 9 or 10, which is a much smaller difference.
Now for the bigger issues:
I do not like the random quests. Elvenar has a jigsaw of buildings as a central feature. This allows for optimization by careful planning, and being able to have MORE success by careful planning is the main reason I like this game (plus the fact it contains no PvP and I can sleep at night without fear of anyone destroying my settlement). Random quests go contrary to planning. And they go contrary to fairness - I may perform worse than my neighbor (or my own settlements on not-so-important worlds) although I invest more time and planning into it, simply because they have more luck with quests.
I guess (and regret) you will not go back to fixed quest lists, but could you make them only partly-random, a bit more fair and plannable? People complaining here about getting the same quests over and over do NOT want a true random system (because true randomness is guaranteed to give some players back-to-back quests when the number of players is high enough). But rather a kind of "cooldown" on quests: Once you have done a quest, it cannot reappear for the next 5 quests. I would prefer a system where every player gets the same quests. I guess I got to be realistic, so ... they could be in an individual order if randomness is really necessary.
I do not like endless quests. They do sound great on paper; at the end of the event you can spend some boosters to complete just three more quests to get that last artifact. But endless quests put a lot of pressure on us. With a closed quest list, I could plan and power through event quests in a week when my spare time permitted it (which I liked) and then relax for the rest of the event (which I liked too). Or I could go slower, knowing that I will get the quests done before the end of the event anyway. With endless quests, there is no relaxing, and going slower always means I will have achieved less at the end. Instead of enjoying the completion of quests, I feel pushed to complete more. I have a job that offers enough pressure, I don't need that in a game.
Also, as you see, in its current form endless quests spell disaster. People are getting 10 evolved bears where you were expecting them to get three. But if you give players the possibility to fulfill endless quests, you must not act surprised if some actually do. That is pretty much predictable. OK, you have several possibilities to stop people from gaining far more than the "border of reasonably achievable artifacts" (no matter whether that border be 9, 18 or 27):
a) Make all quests noticably more difficult. Will affect anyone, not only those few players getting too much. Majority of players will complain quests are too hard, and they will be right about it.
b) Lower rewards of all quests. Will affect anyone, not only those few players getting too much. Majority of players will complain chests are too expensive, and they will be right about it.
c) Double the number of keys needed for each main prize after the "border". Keep doubling every 9 artifacts. Will only affect those you are actually trying to slow down. Of course the affected players will complain about the high costs.
d) Double the cost of keys per chest after the border, and keep doubling every 9 artifacts. Almost the same effect as (c) but affected players will also get less daily prizes, which may or may not make a difference in complaing.
e) Reduce the frequency of artifacts (after the border) among the flow of main prizes: Not every second prize is an artifact, but every fifth only. Again similar effect as (c), but power players will get more expiring buildings to compensate for lower number of artifacts, and less reason to complain.
f) Calculate how many quests are neccessary to reach the border, and after that number of quests done, dramatically cut quest rewards down to 20%. The practical effect is similar to (d), but I think it will generate a lot less complaints. Why? If the costs of prizes suddenly skyrocket at a later step in the prize-gaining process, people will feel betrayed that their hard-earned keys suddenly lose value after reaching the border. But if the quests give less keys in the first place, this clearly states "you have reached the end of regular quests. Proceed futher only as a bonus". My personal favorite.
g) Don't offer endless quests. Easiest way to limit event currency and thus limit prizes won. Rich people can still buy extra currency with diamonds, so no harm done to the company. (My REAL personal favorite, but I think I already mentioned being realistic)