To be clear, Terminator 2: Judgement Day is fantastic and quite frankly the movie franchise should've ended there, but I still don't think it captures the intense, frightening and emotional heart of the first installment.
It's a great follow-up and definitely more of an action film, compared to the sci-fi, techno-slasher first film, but it lacks the impact of the first for two reasons:
In the first film, we get to understand the devasting impact of the war from the perspective of a resistance soldier, Kyle Resse (a character no-one but Michael Biehn could've played). We understand the struggle and fear humanity faces in the future through him, and I love how the future to come is told in the film, essentially in three parts - while they're being chased, while they're hiding and whilst he's being interviewed by Soberman. It's a great way to handle exposition.
The Terminator is essentially a really unusual, but powerful love story of a soldier who is willing to experience the horror of what is to come to protect someone he loves (Sarah) for someone he loves (John), and that aspect of the story really grounds a high concept film, making it (somehow) relatable.
I also think the intensity is unmatched in the first film as Arnie can kind of go toe to toe with the T-1000, whereas Reese and Connor have no choice but to run, and run fast.
Ultimately, there are two great films to enjoy, but I think the first often goes overlooked compared to the more successful and arguably better-known sequel.