I like Stargate too. In fact these days it's the game I'm playing. Though I go back and forth. For me, back in the day, I went from Stargate to Defender because the 7/11 got rid of their Defender and the Safeway on the next block got a Stargate :-)

What I noticed about Stargate back then, coming from Defender, was that it was easier to shoot things. I think this was because the Stargate chip was an upgrade--the faster CPU wouldn't steal time slices from me at odd moments, so the game was more predictable. I remember Eugene Jarvis and Sam Dicker talking about the Defender->Stargate upgrade process at the California Extreme arcade convention in 2014. Stargate is a fun game, and these days I play more casually, not really trying to perfect my skill.

As someone else in the comments noted: Defender is more raw. It's like those characters from the older version of the Matrix: Difficult to kill. It's like Yngwie Malmsteen's demo tape before his first album. There is a basic visceral appeal to it.

Stargate is Defender 2. Some marquees even said Defender 2. It's by Jarvis and De Mar. https://en.wikipedia.org/wiki/Stargate_(video_game)

Legend has it that the reason Stargate is so hard compared to Defender is because the one of the early test units ended up in an arcade where one of the best Defender players in the country hung out; when it came back to Williams with his scores filling the high-score table, they assumed this was because it was just too easy. So they fixed that.