Take Fading Shadows, for instance. It's a good concept, taking your basic guide-the-marble through a puzzle level, hitting switches and changing forms along the way (think of a mash-up between Marble Madness and the Mercury games), but the whole control mechanic of using a beam of light that can weaken or intensify to pull the marble along is where that concept starts to take a back seat to repeated segments of intensely careful movement.
This wouldn't be too bad save for one very glaring issue that was no doubt meant to make the game more fun: to have fine control over the course of the marble (okay, it's actually a single tear shed by an imprisoned boy to fulfill a prophecy and it's sealed inside a protective shell, guided by the boy's clairvoyant sister and... yeah, forget the story), you have to use a relatively strong shaft of light to exert enough pull over the marble. Problem is, if the marble is in anything but in its metallic form, you'll burn the thing up before reaching more complicated destinations.
Those forms include glass (kicked off by hitting Triangle) and Metal/Wood forms only possible by crossing over Transformers that also act as checkpoints. All three forms have obvious strengths and key uses. Wood floats in water, metal can jump/double-jump but rusts in water, glass sinks underwater and weighs less to avoid setting off weight-based triggers, but shatters if hit to hard and will overheat if your beam of light is too strong.
The idea, then, is that you're supposed to scoot this little tear/marble around a level to a shining exit, which is almost always closed off by some manner of switch or chains thereof. This exposes one of the other core problems with the game in that, save for the flyby at the beginning of the level, it can sometimes be maddeningly difficult to figure out where to go or what to do next. More than once I had to completely restart a level (which involves quitting all the way back out to the main menu, then selecting Load Game, then wait through yet another loading screen), and I swear I did the very same actions but somehow the retry would work properly.
It's obvious the game is meant to be a fairly relaxing experience; the music is mostly just ambient loops (which can actually get a little grating, and this is coming from someone who actually enjoys the repetition of stuff like Trance music), and the pace of everything from the beam of light to the movement of the marbles is a slow, languid process meant to be handled with finesse -- except that the PSP's analog nub is notoriously underwhelming as a precision control device (particularly on those launch PSPs).
Given this kind of pacing, it makes having to do repetitive tasks that much more grueling because it all takes so long. Throw in accidental falls off a ledge that, at the very beginning just mean having to scoot around the level's myriad ramps and jumps and later spell instant death, and you've got a game that's just itching to spark short fuses. Had the game been more about directly controlling the marble, it's entirely possible that these issues could have been minimized. I do understand that the developer wanted to do something different, but ultimately it makes the game more painful than challenging.
And it's not like Fading Shadows is without production values. The storyline, while a little trite -- even for a game about guiding a marble into heaven -- is at least told through some genuinely detailed and interesting concept art stills (some of which can be unlocked by finding puzzle pieces scattered throughout the levels). The graphics engine, too, sports little touches like a depth of field filter to blur out foreground or background objects, though the game's draw distance during pre-level flybys is a little weak. This can also lead to the framerate chugging a little early on, though when playing the main levels it's actually rather solid.
The camera, however, tends to hurt more than it helps. The slow, swinging way it can be panned around fits the pace of the game, but again, it can make retrying sections needlessly frustrating. One particular example is an early puzzle where you have to roll across a floor with numbers. It's hard enough trying to guide the marble around by its light leash, but when objects get in the way of the camera or things suddenly shift, it can lead to accidents or even cheap deaths. The game is forgiving in that it offers a free life for every 10 gems picked up in a level, but it only goes so far.
The game's multiplayer features are about as broad as you'd expect from my rather chilly reception of the game. It effectively takes a random level and drops you and an Ad-Hoc player into the same stage in a race to get to the finish first. Do that and you get a point. Get three points and you win the multiplayer "battle." Since you can see the other player's shaft of light (their marble is translucent), it actually makes an already confusing game even more frustrating. I suppose it could be a test of one's precision jumping/speed running skill, but for me, it felt mostly like an afterthought.