Hello, first off - a very nice game, grindy but still enjoyable.
And to suggestions:
I am yet to get to 20lvl of orcs and don't know the later pace but 1) there should be a way to increase gain at earlier lvls... This 1/2 gain untill 100lvl is quite insane... i think it will take me around 1 month to get to 50lvl and that's quite long to keep people hooked at current pace. Maybe some more cheaper Tower upgrades (and earlier bonus damage for them) will do the trick of better feeling the progression.
2) Game auto-start with choosen buildings and options, towers auto-build near the existing buildings or Core. <-- this will earn you lots of love from players i guess :)
3) Overall QoL - buy all cheapest upgrades button (except for gold, as it is used to buy options before the game). Sometimes i just want to equalize things price-wise.