Witcher One is just as diverse, even if its an older game and obvious issues come from that. Subtle choices affect and change the plot as often as big ones. Actually I would say that Witcher One is both longer and shows you a wider number of areas + monsters.
I felt Witcher 2 got completed abit too quick even if it was great.
I would certainly advise playing it though you'll find the combat system from Witcher Two was redesigned. After playing Witcher One, Witcher 2 threw when it came to combat, even if I had imported my character and some decent weapons and armor lol.
Scoia'tael all the way! *puts on bandanna and his squirrel tail fur cap*