I have some fond memories of playing both the arcade and Atari 2600 versions of Defender. As one of the first sidescrolling shoot-em-ups ever made, Defender has you in control of a spaceship that flies back and forth over a city while shooting down alien ships. It's a simple concept made more complicated by the fact that certain aliens, the Landers, will attempt to kidnap your planet's inhabitants and turn them against you.
Now, I remembered Atari 2600 Defender being a pretty good game from what I played of it in my youth, but when I recently popped it in my 7800 and gave it a whirl, I had flashbacks to my experience with the Sega Master System game, Hang On. On my first try, and with very little effort, I played one game of Defender for about two hours and rolled over both the stage counter and the score. At that point, I had a ridiculous amount of lives in reserve and could probably just have played forever without any danger of ever losing them all. I turned the game off and contemplated what was wrong with it.
The biggest problem is that it's much too easy to earn extra lives. Since Defender has several pointless difficulty variations (most of which involve starting at a slightly later stage), an idea that would've been nice is a variation that gives a "no earning extra lives" penalty, but alas, no such thing exists. Accumulating a large amount of lives in such a short time frame needs to be countered by increasing difficulty in elements of the gameplay, but that doesn't happen here. The number of enemies and the types that appear in each stage never change. The Landers become faster at kidnapping your people after a few rounds, making it much more difficult (if not impossible) to fly to where they are, shoot them down, and then save the hapless humanoid from plunging to its doom. But the aggressiveness of the other enemies, particularly those that exist for the sole purpose of seeking out and destroying your ship, is never increased to where they become any kind of a threat. As such, most deaths in this game come from accidentally turning around into a bullet that had just been fired from an enemy that just appeared off the side of the screen. Everything else is easily avoided.
There really isn't even enough motivation to protect your people. The penalty for losing all of them is that you fight rounds of nothing but Mutants until you reach the next stage that's a multiple of 5. That's not very heartbreaking. The Mutants all line up in rows, making them easy targets. While you can rack up a lot of points by rescuing your people and having some alive at the end of a stage, it doesn't really matter. Just by playing the game long enough, the score will eventually roll over regardless of what you do.
I don't think this port is anywhere near as botched as that of the Atari 2600 Pac-Man. At least it looks and sounds pretty good, even though the mountains of the arcade game were replaced with skyscrapers. But I cannot think of any reason to play it except for nostalgia. Almost any other home version of Defender has been more true to the frantic action of the arcade game, but for a better game of this type on the 2600 itself, try Stargate, aka Defender 2.