The reactor is currently a weak part, yes- the tutorial used to mention that about the coolant, but I scrubbed it when making it much less verbose. (Removed it in current progress.) The reactor is definitely going to be tweaked.
For the left/right hand, I'd like to eventually enable mouse-only controls, but that's lower priority over content and fixes. It does take some getting used to- I might add left/right indicators, later on, to help track what's where.
I am planning to make the entry/exit much more detailed, with middling frames before it's inside- this just requires a lot more art to accomplish. Internal view is a good idea, but hard to implement- I'll think about that one. A lot of enemies is partly the focus, at least for now- but I'm planning to diversify once I have more groundwork laid out, so there's room for different tastes.
As for the worms acting like 'popcorn', are you holding them in? They can be kept around by blocking their exit- best done by only enabling Chest + Crotch, and clicking said bodyparts. (Which, of course, should probably be explained before the dreaded reactor, instead of after.) Other than that, the current implementation is easy to change- it'll probably be tweaked as time goes on.