For me the main issues were with input and feedback. When I tap a direction key, the game often moves me two or more times. The character movement and camera movement are both instantaneous, which makes it difficult to tell how I moved (the message log helps with this, but it could do with a more readable font).
I couldn't tell how to shoot the aliens when they appeared; only the movement controls were described, and bumping into them didn't work.
This is just a pet peeve of mine, but cursor key controls in an isometric game don't make sense to me because of the 45 degree rotation. I hear there exist people who are OK with that. *shrug*
In light of the difficulties controlling the game I can't really speculate on what might be "missing" - perhaps when some of the kinks have been worked out. I also have only the vaguest memories of AliensRL from a brief playthrough and watching one of Game_Hunter's videos of the game. I'd say the things that stood out to me about that game in particular were the management of constrained resources, the care needed to take enemies down safely, and the balancing of risk/reward in deciding which parts of the base to explore.