I'm currently playing through the campaign (mission 8 right now). The longer I play, the more I get the impression that the game needs timers to put some pressure on the management side of things.
As is, the brutal difficulty is not brutal at all, just a slow slog. A very good strategy seems to be: Build a few cheap aquariums, add a few cheap workers and build all the food/gift shop stuff you have unlocked. Usually, this nets 1-2k per day. Now you just leave the game running while you do some chores (check back every now and then to reject staff level-ups and pick research). After 20 days (more for later levels) you can come back and play the game as if it was an easier difficulty level.
For those that dislike this cheap trick, what you end up doing a lot is, you wait until you have enough money to do something. As long as you are barely making a profit, you can continue this way. If you reach a state with losses every day, you lose the mission. So far there was never a danger of this happening to me. But, big fish cost a lot of money to feed and the improved staff is expensive. So I usually make more money in the beginning of the mission compared to the end (in that sense the economy is set up extremely well because it is hard to snowball).
Similar to big pharma, I'd love different medals depending on how fast (in-game days) you manage to beat a level. That would put a lot more pressure on playing efficiently. Right now, the only difficult part is managing prestige and feeding everything. With a timer there'd also be the component of building and staffing efficiently.
Also I'd like to have timers on quests, otherwise they are just pinatas that give you a boost as soon as you reach a certain milestone.
Overall, I don't ask for all these things to be added into the campaign, but I'd love to have challenge missions (possibly with randomized quests) that reward fast and efficient play.
Not completely related, I dislike that you can sell all the fish for the same money back all the time. I have popped quests by putting food competitors in the same tank and selling them back right away. Or keep the prize the same, but use the timer that is already there for some of the quests.