I'm still playing casually, having fun building out my Plankerton Storm Base, just dumping resources into it everytime I hit 1k/1k/1k. I dont even care how efficient etc, I like the Fort Building aspect, I'm building crap i know won't even matter but it looks cool lol. Also upgrading everything to level 3 which is the real resource hog.
I'm around level 25 now, haven't spent any money other than Box cost, I've done up to level 40 missions where you need to defend 3x Atlas at the same time (build 3 forts etc). It does get more fun but getting there just takes a while, and I certainly do not like the Loot Chest system.
I just got my first Mythic (Survivor) from a chest, also just got my first Legendary Trap (gas ceiling). Still only have Epic heroes and my main Soldier hero is still only Rare. I have an Epic Soldier but need Pure Drops of Rain and I probably don't want to use them on her yet anyway.
I run 1-2 missions a night, setup my offline resource gathering shit, build up my base and then play a different game... Missions usually take 30mins each now because of the constant resource gathering that takes forever.