That was the case in the first two games but they changed things a bit in Chaos Theory. The AIs are somewhat smarter and at higher difficulty levels you can only take one or two hits, so fighting is rarely an option. Actually, in CT I only killed three or four guys in the entire game, although that was mainly because I wanted to see what the guys said when you captured them.
(almost every enemy in that has a unique conversation)
Can't say I was such a huge fan single player of SC. Decent cinematic feel to it but the missions felt a little scripted, like you had perform a specific trick to continue. Where as something like Thief where you could choose how to overcome obstacles.
I know what you mean with respect to the first two games, but I thought CT was much less linear than those. From what I'm hearing about this new game, it looks like it's still more nonlinear and is supposed to have a couple of different endings. Now if only it would run decently...