I'm glad the update is bringing more content. I've played through the game and $15 felt a little pricey for what I got out of it (felt more like an $8-$10 game). I'm hoping the extra content will make the $15 tag worth it, but I'll have to wait a few months to find out.
Personally, I'm hoping to see more Breast Expansion content, particularly since the demo didn't feature any. (Something you should probably explain on certain other sites the game is being advertised on. The demo is tagged fine here.)
I saw the stairs mentioned in another comment, so I won't reiterate on those. I do think more could be done to indicate the thresholds for the level bonuses in the main menu. I had little reason to use more than the pistol in most cases, with the other cases being defaulted to the Jupiter Cannon. The Minigun didn't really fire fast enough to seem worth using over the pistol. The Glue Gun felt like it was essentially a melee with extra range.
Two major annoyances I wanted to bring up. The mostly invisible enemies are... They feel kind of uncalled for. Once you know they're there, they are less of an issue. But it's still a gut punch that isn't fun to deal with. I think they and the scientists should be excluded from the spawn list in the boss level. I get why spawns need to happen there, but the invisibility and how scientists attack are both quite annoying on top of everything else that happens.