Really fucking great!
Ended up with this monstrosity and got to 51 before I quit
Never bothered using a second gun, although I considered making a pure bullet breaker...
If there was a "combine all" button and/or sorting on the modifiers I would have, but it seemed like too much of a hassle so I just stopped paying attention to new mods I got.
It also seems like the lower-tier mods might be too good? This baby clocked in at 1,837 dps with bullets that flooded the screen then all tracked to whatever enemies were alive. I'd pre-flood the screen then kill every enemy within seconds, the guys who shot bullets on death being the only threat.
I'd specifically look at the balance of the costs, maybe making some of the low tiers cost more and high tiers cost less. But I only did this one run so maybe you can make even MORE broken shit with high-tier mods.
There could be better audiovisual feedback on enemy hits/kills. The "pop" sounds too... friendly? Some kind of quick bleepy explosion would be cool. And maybe flashing a color on hit. The explosion visual could also use a bit of work, it feels more like the enemies just pop out of existence than "exploding."
I don't like these kind of late game scenarios where the player basically gets too strong to lose and the game can never catch up. Some devs/players do, so you might not want this advice, but I think making enemy damage scale, or enemy health start scaling exponentially per wave would do the trick. Or both.
My game happens to be... remarkably similar, so you might be interested in ripping off some of my "support items" for some of your modifiers. I know I wrote "bullet shrapnel" and "bullet ricochet" in my notes after this session.
Also, great job on the fucking optimization dude, real nice