Difficulty was far too high. I too got around three quarters along before the difficulty became so bad that every click was taking me backwards. The -10km each time you lose is a disincentive to keep playing. You have to win at least 1 out of every 3 goes otherwise you end up going backwards and losing any progress made. Levelling up was no use either as the enemies just got that bit stronger. Without accurate records, I cannot prove this next claim, but I am fairly sure that on almost every round there were more enemies that had enough power to eliminate my players in one hit than my players that could eliminate an enemy with one hit. My team was ALWAYS more easier to take down with single hits than the enemy was.
The boxes took too long to open, unless you used PP, given the duration of the game. Boxes should open either for free or at reduced cost in the final hours - these boxes have already been WON by me, its not a free gift, or there should be an option to continue to collect your rewards after the game has closed.
There were too few box slots. There is no incentive to keep playing if you cannot hold more than 3 boxes. Once the slots are full, there is no point in playing further with the risk of going backwards coupled with the lack of significant reward for doing so (the XP awarded was not enough to help move reasonably quickly up levels, given the overall duration of the event).
I understand this was based on some kind of "top trumps" model and think the probabilities of winning and expected returns should be made clear to players so we can make informed choices. The majority of players have some understanding of the TW game mechanics and use this knowledge to play effectively. To ask us to then play a game where the chances of winning and game mechanics are kept secret does not fit with this.
Right now, I'm not sure it was worth the time, effort or PP. I will certainly be more reluctant to play these in the future as I do feel fairly short-changed now this has finished.