the hatch was like 5 episodes in, the smoke monster was in the first episode, ghosts were in the second, rousseau was early on, the others, polar bears, power sources, prophetic visions, etc. you should re-watch season one and see just how much really was laid out -- it's also a bit six-senseish to do so. like an entirely different experience (christian's ghost wore white sneakers!)
obviously there were story arcs and flips along the way, and things like mr. eko being a shit or ben being an awesome, but i think it holds pretty true that the overall show had a definitive map. and, through writer's strikes and renewed contracts, they just had to ebb and flow how much new content to create in the meantime.
