A great update all in all. Seems like you took a lot of community suggestions to heart (You already had a lot of this planned earlier, I assume, but it's still nice that you added stuff we wanted to see).
Really love the EM Railgun, it just feels so powerful, like it should. The Scattergun is also nice but the Railgun just overshadows it in terms of pure joy. The new FX for the missiles also look really good, definitely an improvement over the last version.
The new mission is really fun to play. The new attack helicopter provides a fun challenge, and the WW1 looking tank thing is a really nice addition as well. To me it also feels like the AI of the old enemies has changed. Could just be me though.
I guess the only thing that annoys me about the new enemies is that you can't see the helicopter when you're running away from it while it's shooting at you.
Another thing is, I really love how OP the Railgun is, but currently it's just that, OP. It takes makes the game really easy, if I'm being honest, though maybe I'm just playing the game wrong. Maybe reducing the ammo further would help? I'm not sure. Using the Railgun also makes the viewport seem really small, since you'd want to use it from as far away as possible, but that's not very far. But increasing the viewport size for just the Railgun would make it OP again. I don't really know how to fix it, I'd just like to express what I thought while playing it.
Apart from that, I'd like to play the game in windowed mode even at 1080p (I mean, you can use Alt + Enter, but that looks really janky), but apart from that, this update seems really high quality. It makes me really excited for what the future holds for this game.