At the time it was released, yeah. It was insanely intense and terrifying. It was not like a classic so-called "horror" film. It got you invested in sympathetic characters and used its claustrophobic setting to maximum effect. And it had blood and guts. Not at all the same thing as Bela Lugosi and "I vant to dreenk your bloood!"
In the last 30+ years everything that made it so scary has be re-used and badly done and OVERdone. You can get the blood and guts on network TV now. Its iconic scenes are now practically comedy punchlines by comparison since even Mel Brooks spoofed it on screen.
When it first came out I went to see it with a friend who'd already seen it. HE spent the movie watching through his fingers. It was far and away more intense than anything I'd seen up to that point (next closest was probably Jaws, and no comparison) and I had to insist that he start warning me when the real scary parts were coming up. If I went to see it now for the first time having been very well inured to all of its techniques, yeah I'd say that it had a couple good "gotcha" moments but I would have likely wanted more action.