UI ergonomic is terrible.
All slots/icons MUST be clicable. These slots are 3-8 times larger than buttons. Empty squad slots should open "reqruit" window. Weapons/items/power-ups should open corresponding selection window. "Unselect" button on "item select' screen should be same as "items" buttons (maybe call it "empty" or "use nothing") otherwise it's hard to find. Or just unselect an item when player clicks on used slot (first proposal is better).
There should be no separate "shop" window. All shopping should be made from an "item select" screen. Just display either a number of remaining items or a price for a new item. If you want, add small "sell" button under an item (buying is performed by clicking on an icon itself).
Mission objectives should be reviewed before or/and after a mission. You should easily know, which tasks are complete and which are not.
P.S. Are "double bullet" upgrades cumulative?
 "Cobra Squad 2"){kind=icon}