I suppose it sounds good in theory at first, the idea that you could simply release parts of a game over time and if anyone wants to partake in the experience they can simply wait from 'chapter' to 'chapter'. Surely if anyone enjoyed the first experience, they would then go on to partake in the second (or third) knowing full well what they're getting into. Best of all the developer makes a little extra cash, as multi-part games are (more likely than not) going to be downloadable first and foremost. It all sounds great on paper, but put into practice it's hard to think of any game that sold better broken down into smaller sections than if instead sold in one larger final product. In fact, it typically has the reverse of the intended effect: the games generally get worse as time goes on.
It sounds cruel to say, particularly considering that developing a game is no easy task. But when focusing on a single goal it's easy to see where the natural life cycle of a game starts and ends. A character goes through the tutorial level, learns the basics and slowly the game expands upon those items/weapons/moves/gimmicks until the player reaches a satisfying conclusion. There is a very clear start and finish, and it's here where the developer's skills are truly tested. If they can hold a players interest from beginning to end then they've done a good job. If not, well then they can take that opportunity to sit back and learn their lesson.
It's here where having multiple chapters really hurts the development process, since it's far more difficult to tell where the improvement needs to come into play. Is each chapter a full game? The marketing teams will describe it as such, but I hate to say that Sonic the Hedgehog 4 Episode 1 is a particularly compelling experience. How much accomplishment can a player truly experience in just a few short levels, particularly knowing well in advance that the experience isn't even supposed to be over?
A multi-chapter game isn't to be confused with a sequel either, those are two very different things. Here, it's clearly defined that the game will be broken down into different parts. What springs to mind immediately is a final product, split up into separate sections, but for purely the developer's financial convenience. How can any development team possibly improve from chapter (or episode) to chapter? The bar is already set, and beating it right off the bat would beg to ask why bother splitting the game up in the first place; but on the same page having an entirely new episode seems to mean that the entire formula needs to start all over again. The difficulty must be reset, and the feeling of level advancement must be redefined.
A fantastic example of this issue would be the Alien Breed series, which starts off with much hope and promise but rapidly declines as players come to realize the experience never really changes. If combined into one big game (with a few additional tweaks for balance) it would be an entirely different sort of beast to play, perhaps even a success in some ways. But broken down into three similar-but-different parts? There really is no reason to play beyond the first.
Another great soon-to-be example is StarCraft II, a franchise that will have to work extremely hard to prove that it's worth buying for a second time. Things may be different with this RTS as the PC gaming community is more willing to accept the idea of an expansion pack, but the fact remains that outside of a single player storyline there is little a 'Part 2' could offer that really couldn't be offered via content patch. Part of Heart of the Swarm's difficulty will lie in explaining to players what the value of such a product, be it a full fledged expansion or simple content update, really is.
Perhaps the industry just needs a little more time to create a multi-chapter experience that is truly worthwhile experiencing, something that will set a standard for this style of gameplay. If that's the case, I wish those developers the best of luck, because they'll have a lot of work ahead of them attempting to prove that their series isn't just another cash grab. In the meantime it would probably be best if we put these kinds of games to rest. Developers, after all, should be striving to create the most complete, finalized games and work from there. Not just deliver a series of very similar experiences.