I was always in love with the Jupiter Lander/Space Taxi physics-based steering and there's never enough such games for the 8-bit machines for me. Enjoyed your game a lot. It's a very solid unique idea, equally well executed. It sort of feels like the launch titles, creating a genre in a way. Well defined mechanics, with simplified, but neat and informative schematic graphics.
There is one thing tho, that I've found lacking. Variety of gameplay. It's just the same wrestle every time and would quickly grow old. Therefore, to keep with the spirit of multiple "games" within one, like with the early cartridges (Combat, Air Sea Battle, Video Olympics), I'd like to give you some ideas to make your creation much more attractive.
Including multiple new game modes, while keeping the original rendering engine shouldn't be that hard. Many of those would require some kind of numeric score counter tho, but I think it'd be worth it. To cheaply introduce even more variations, you can make the difficulty switches change the behavior of particular seemingly small details of the gameplay, like - will the Lander bounce off the walls in a predictable manner or totally randomly.
From what I've read, your game's code only takes up 2kb, so there'd be plenty of space for new modes and maps within the non-bankswitched limit of 4kb.
Introduce some of those, or maybe come up with your own under my inspiration, and you're not only making one fan happier, but also can make it to Atari 2600 hombrew history. I feel that this game's simple premise and brilliant presentation have a lot of potential. Here's a couple of ideas for starters.:
Tag. (Like many of the below, heavily influenced by Indy 500.) One of the Landers is flashing, meaning he's the fugitive. The other has to catch him, to prevent the first player from accumulating points. Once the fugitive is caught, players switch roles. Points are awarded only for the escapee and are proportional to the time spent running away. One point for every second of escape. On Tag variant of the game, the Landers are indestructible and will bounce off harmlessly from the walls. Once either player scores a sum of 99 points, the game is over and the winner flashes as a visual indicator for victory.
Deadly Tag. Like the Tag game above, only players are no longer invulnerable to collisions with walls. Crashing into wall will cause a loss of the fugitive status (players instantly switch roles) or a short stun for the chasing player.
Collector. Players compete to reach a randomly placed object (say a small square representing some space trash or meteors) and are awarded one point for each. Once the item is collected, it will reappear in another random location, always only one piece. On Collector variant of the game, the Landers are indestructible and will bounce off harmlessly from the walls
Deadly Collector. Like the Collector game, but crashing into walls will cause a short stun.
Cave Run. Players have to navigate a one-screen maze. Whoever reaches the end first is awarded a point and the map is reset, with player's swapping starting positions (to prevent the advantage of starting closer to the inner side of the curves). First player to reach 10 points wins. On Cave Run variant of the game, the Landers are indestructible and will bounce off harmlessly from the walls.
Deadly Cave Run. Like the Cave Run game, but crashing into walls will cause a short stun.
Ideas for Difficulty Switches' settings:
Super Inertia. The Landers quickly gain a lot of inertia (say twice as fast as the original steering). This will mean a completely new, more thrilling and precise experience for the players.
Random Bounce. Landers no longer bounce off the walls (in supported modes) in a predictable manner, but completely at random.
Reverse Gravity. Self-explanatory.
Wraparound movement. Have some maps lack vertical or horizontal walls, or even have openings in both dimensions! Players leaving the screen thru one edge would emerge on the other side. With smart layout, some crazy combinations could be achieved. A must have!
Variety in Landers' graphics. Perhaps have the different game modes use distinct Landers' sprites? Collectors being more chunky, Tag ones more sleek, etc.
Phew, sorry for the wall of text, but I just wish this game gets released as a more complete product, providing hours of entertainment.
Imagine writing like "27 video games" onto the box, now that's something to be proud of!