I didn't find it as easy as you, but that may be down to either lack of skill in these kind of games or just a different method of playing. I kind of hoarded the energy bars / packs unless I couldn't progress without them, and that meant rarely cloaking as I wanted to sneak up behind every individual, knock them unconcious and drag them aside and never be seen.

I'm really keen on replaying without caring about not being seen etc. though. I think it'll probably be a lot more fun. =]