The pacing of a game. 

Basically it's how fast or slow things happen in a game such as getting more powerful items or weapons in a game at the necessary time, how the story progresses, liesure time (getting to mess around with things doing sidequests, minigames and talking to NPC's), and of course the balance of the gameplay to where it doesn't become too much of a hassle in overdoing or underdoing something.

The pacing is all of these things combined, and if properly done can make a game perfect in someones eyes.  After a long battle in a game, you might want to mess around with minigames and sidequests.  The events of a story need to correspong with the gameplay at the right intervals, ex: someone dies in the story so the main character or characters get more powerful or a new ability to make things more connective to the player.     

Half. Life. 2.

The pacing and structure of games is overlooked and yet its one of the most important aspects of a game. I find usually though its pretty much okay in most games.

I found HL2 to be one of the worst games for pacing, they have action then long boring parts which seem to add nothing to the game, besides to take up time. Now i found CoD4 to be one of the best paced games. But thats just me.

Pacing is going to vary according to what you want.

For example from my point of view COD4 has no pacing in the traditional sense as it does not convey a story with traditional arcs, etc. - i.e. each level is distinct from the last and complete in itself, while each level employs a simple pacing tactic of increasing difficulty / impact through to a climax.

Half Life 2 has pretty good pacing in terms of story arc balanced with gameplay as does Halo.

But that's because I prefer story led experiences to pure gameplay led experiences - which is just me and not some universal truth.

Call of Duty 4, the intensity of the firefights generally started to build up and up through the story, and each level was linked together. The great think in that game was after a very intense section, you got to play in the AC-130, which was just so relaxing in comparison, and you can just lean back and easily take out tangos, as opposed to having to fight for your life constantly

For the most part, I'm satisfied with pacing in my games. Games like Silent Hill, Resident Evil, and Halo 3 are really good at anticipation vs. reward. A ton of games, from Star Fox to Zelda to Metal Gear get it right. It's when a game like Max Payne or Stranglehold come out, where it's pretty much nonstop action, where you really appreciate the absence of good pacing. Nonstop action is boring. Go figure.

I hadn't really considered pacing as a big aspect of a game... but what you say is true. Without proper pacing the game can only be so good, which can still be awesome none-the-less. The thing with pacing is everybody wants something different, and pacing is not entirely hit or miss. Pacing can be good at times, and at others need work. Rarely does a game designer implement such poor pacing that it breaks the game.

d21lewis : yeah , I found the pacing in RE games to be pretty good . Also some older RPGs have great pacing to , especially PC RPGs ...