Yeah, that's definitely my favourite part of stealth games. Watching from the shadows, studying from perches, peeking around corners. Really just monitoring your prey. They did a good of translating that stuff into a 2D environment.
You'd probably like Tenchu as well. It's pretty much just this game in 3D, only with lower production values lol. Nah it's good though. Pick up Tenchu Z on the 360 if you get a chance, it'll be dirt cheap by now.
I agree with Barakah, Tenchu Z has horrible graphics and they reuse the stages but the gameplay is surprisingly refined and fun. I thoroughly enjoyed that game and will continue to keep it in my very small library of games.