Late-night video game ponderings
Fallout 3 has had me thinking about nonlinear games and their pitfalls. Don't take anything in here as recommending that anyone skip Fallout 3 if it sounds interesting. It's a good game with high production values. It just didn't hold my interest as long as it could have. The Zero Punctuation review (http://www.escapistmagazine.com/videos/view/zero-punctuation/420-Fallout-3) pretty much nailed its good and bad points, in the usual NSFW fashion.
One of the big ones is variety of gameplay. There can be a hundred different places to go, but if you're going to do pretty much the same thing no matter where you wind up, the game stops being interesting long before you explore them all. Fallout 3 had this problem to some degree. The game gives you a few different ways of engaging enemies (sneaky or heavily armored, and a few different types of weapons) but once you've gravitated to one, you generally use it just about everywhere. Character interaction ("quests") can help break things up, but too many of the places you'd stumble into in Fallout 3 were thump-and-scavenge affairs. The previous Fallout games from Interplay didn't suffer from this as much, I think, while the previous Elder Scrolls games did, unsurprisingly. GTA 3 was pretty good about offering different kinds of gameplay in different parts of the sandbox, although some of them were awkward.
Variety of graphics can also suffer from the production demands of making big worlds. Morrowind's world was richly developed in concept, but graphically it was uniform, alien, and bleak, making it a litle difficult to care about the fate of Vvardenfell. Oblivion did a better job in this department, but Fallout 3 backslid to some degree; there isn't a lot out there besides ruins, vaults, and subways.
Lots of nonlinear games struggle with the difficulty curve. If you can go anywhere, what happens if you go straight to the fortress of the big bad, or somewhere equally far along the main plotline? Is it okay for 90% of the world to be much too threatening to a starting player? Oblivion took the unusual approach of making enemies level up as you do, which meant the world was about equally difficult no matter where you went, and the difficulty of the game depended on how well you minmaxed the character development system. If you didn't know what you were doing, levelling up could make your life substantially more dangerous even in places you'd previously been able to handle. Fallout 3 took a more tempered approach; humanoid enemies are better equipped as you gain levels, but enemy health depends purely on type. So you aren't ready to take on super mutants and deathclaws at the start of the game, but raiders can still be mildly threatening at max level even though you've been able to kill them since level 2. I'm glad that Fallout 3 backed off on the automatically-adjusting world; I prefer the sense that levelling up increases your ability to take on challenges you couldn't handle before.
The reward curve can also be wonky. In Fallout 3, you start out scrounging for the bare necessities to survive, but then after a while you build up a huge surplus, to the point where you could really start to care less about all the stimpacks and ammo you're picking up. Levelling up also felt pretty linear. Too many of the perks boiled down to "increase this stat or skill by a few percent"; there wasn't much sense that they were allowing you to do things you couldn't do before, only the same things a little better. Other games have done better in this regard, even previous Elder Scrolls games (in particular the nonlinear "mastery level" benefits when you level a skill to 25/50/75/100 in Morrowind and Oblivion).
Perhaps the most subtle pitfall is the game music. A linear game is in control of its pacing and can fit the music to match. Nonlinear games often fall back to "relaxing" and "exciting" music, sometimes with jarring transitions, or will delegate control of the music to the player rather than the game (like GTA 3's car radio or Fallout 3's Pipboy radio). It's easy to gloss over the quality of a game's music, but most of video gaming's timeless favorites have had great music tracks--and sometimes not a lot more.