So far this is looking very promising - nice work! - but it looks like it still has some bugs to iron out too, unless they're emulator issues. I've never used RVM before so I don't know how it is for accuracy.
In terms of bugs, here's a few things I noticed, a couple of which have been mentioned already, but maybe it'll help to repeat how they occurred for me. The list has ended up surprisingly long, so sorry about that, and I guess some are so obvious you'll already be well aware of them anyway, but you asked for feedback on bugs, so, I am obliging.
I've had 3 occasions where the screen suddenly 'rolled' briefly, as though screen sync was lost for a frame. Only the play area dropped downwards, the score panel remained where it was. For what it's worth, on at least two of these occasions, I'm fairly sure it coincided with something blowing up.
Possibly related, I've also had the game flat out crash just when I died on one occasion. I've attached the SNA from RVM in case that's a help, but probably not.
The first hexagonal white moving enemy that appears on the left of the screen seems to always leave a row of rubbish off the side of the screen, 4 pixels long and 1 pixel high.
On one occasion, I believe I destroyed the last ground emplacement on the right edge of the screen just before the boss and it did not leave a crater. The game was a bit busy at the time though, so I can not be 100% sure that it didn't alternatively not place the turret at all. All I know for sure is after all the enemies were cleared, the space where that turret should be was 'clean' with no wreckage. This has only happened the once though, maybe I was imagining things...
The last two aren't necessarily bugs and might be me just not liking how it is, but anyway.
On one occasion, I picked up a star on the very right of screen. This got me to the missiles, so I pushed fire 2 to activate it. This moved the ship to the left automatically, picking up an additional star that happened to be sitting to the left of the one I'd just collected in the process. The game then moved the power up selector to the shield and gave me the shield when the ship stopped auto moving. I don't know if that's how it's meant to be working, but I'd prefer to get the power up I selected when I pushed fire 2, regardless of if the ship then collects another star after that during an auto move. Of course this also only happened the once, so again, maybe I imagined it.
Collision detection - several things. Not sure how easy it is to adjust but I have found a few different things that feel a bit off with it to me. They are:
The standard player shot can pass through the left side of enemies. It's most noticeable with the blue stationary enemies, where if you fire a shot to the left of it, the right player bullet can pass right over the enemy without colliding.
Conversely, I have found that the player can sometimes pass almost halfway over the right side of the star pickups before it registers as collected. This can seem even more obvious when the ship has been enlarged with the first of the 'widen' power ups.
Final collision issue. When using the very fast laser, it does not seem to be hitting enemies just in front of the player.
