Well, I AM old enough for the original Deus Ex
But I thought the same as you at first. I played the demo, which IIRC was just the first level (liberty island), and I was pretty bored by it - it all seemed very slow and clumsy. But, when the reviews of the full game came out and universally sung its praises, I thought I'd give it another chance, and bought it. It's a good job I did too, because once you give it a chance it turns out to be a masterpiece - possibly still my favourite game of all time.
I guess that it has aged a lot now, so might be even harder to get into, but still - well worth giving it another chance. The first level really doesn't represent the quality of the game, which is all based around the awesome story, and the dialogue that develops it.