I made it to level 33 and the gameplay is very fun and addicting. The game's visuals are appealing and I like the little details as well such as the background reacting to the player. The challenge is there and at no point did I feel it was too hard or easy. The mechanic of mixing and matching modifiers is great especially the part where upgrading modifiers can allow you to save on the cost limit. Finding fun combinations such as rapid fire to take care of hordes or a slow, homing missile that can two-shot enemies is great and specific enemy types (like the orange ones that spawn bullets on death) makes you think twice before shooting at the enemy spawn. More modifiers would be fun to see.
The modifier list is great with different colors to distinguish types. Because of the colors, it wasn't a big deal scanning through the list but a sort feature could be helpful. Also, having certain buttons to auto remove modifiers from guns or the crafting slot (like a right-click) could speed things up, but clicking and dragging was barely an issue.