it might just be me, but pacing in games with a single core mechanic (such as combat) are very hard to do right from a LD perspective. I got combat fatigue from playing halo because there was too much combat, which is probably not the intention of the developers. it seems a given that combat should just be combat and in these run of the mill fps times, nobody really gives a fuck about good gameplay anymore as long as shit sells. brands have taken the place of good games.
i don't want every game to be emergent like stealth games, but something as simple as a counterweight to the combat mechanic seems necessary. i don't think i would have played half-life 1 to the end if it wasn't for the amazing pacing and balance between combat and puzzles throughout the game.