A good interface? Really fast?
Maybe it had some unique feature you've not seen in a browser since then?
It might be "obsolete" today, but I'd like to know anyway.
Me, personally, I'm a big fan of Opera 3.x/3.62 for its insane speed, Safari 3.x/3.2.3 on Windows for its clean design, and Netscape 3.x just for the nostalgia feeling.
I also liked Trident IE (4.x-11.x) for how "Windowsy" it felt, with the widget appearance and keyboard controls following the Windows design language to the pixel.