Before you read this, please keep in mind that I use the word 'problem' very loosely. I wholly enjoyed this game but there are some nagging details I will go over shortly.
Now, the plotline of Portal seems innocuous at first. You're just your average ordinary dude who winds up waking up senseless in a tiny room with a too-friendly computer voice talking at you while elevator muzak warbles from a tiny radio set not a few feet away from you. Okay, that's fine. It's even funny at times! Let's progress a bit now.
You find yourself moving through a scientific laboratory's test chamber without the slightest bit of backstory, and normally that wouldn't be a problem, but the friendly voice accompanying you offhandedly lets you know that it's not your first time through this test. A minor plot hole, acceptable when considering the jocular tone of the game, but again, problems arise further down the road.
It is aboutt his point that you find out that the protagonist is a female dressed in an orange jumpsuit with what seems to be fake feet attached to your real feet. This also is unsurprising, but what comes next kind of threw me for a loop.
The aforementioned voice calls you an android! Is this a fact? A red herring? Something to throw you off the trail, or is it a bona fide plot twist later yet to be revealed? You don't know either way as the player since it's again a very offhanded comment slipped in amongst other humorous lines of dialogue with an air of sinister levity. This fact is never brought up again throughout the course of the entire game. Why would it do this?
Let's set that aside for a moment. Let's evaluate what comes after that for a moment, on a purely psychological level. This voice slowly but steadily becomes more and more desperate and deranged as the game progresses. As I've stated before, this isn't a problem until you couple it with all the events mentioned thus far.
What does your lovely antagonist do, you might be wondering at this point? Trying to dissuade you in a vaariety of ways, including reverse psychology, double reverse psychology, triple reverse psychology, bribes, and even direct threat. When you go over this voice's dubious record, it makes you question its initial motives. Is it crazy? It sure does seem that way. Is it desperate? I don't know! Let's delve yet further into th epsyche of our mysterious antagonist.
Later on you chance upon the heart, sou, and source of this mysterious, unnerving, yet ultimately ineffectual voice that's been accompanying you for the entirety of the game. It's a machine named GLaDOS. It lives in the center of a cylindrical room and it appears to be very complex.
When you encounter it, the first thing that happens is you witness the thng dropping its morality core. One can write this off as mere comedy. Past that, however, there exists a curiosity core, a rage core, and an analysis core. I think that's what the blue core is, at any rate. Anyway, after you dump them all into the suspiciously positioned nearby incinerator, the machine which has GLaDOS labeled all over the sides of it falls apart.
You start travelling upwards, which is a very disconcerting motion to travel in even in light of the game, and you eventually find yourself on the surface. Then another scene occurs where you discover that there are any number of GLaDOS cores laying about in a nondescript warehouse, along with the cake that it tried to bribe you with multiple times throughout your journey.
This leaves the player with a question: Was what the player just went through a very elaborately designed test, or was it a legitimate escape through a complex controlled by a deranged computer? There's no way of knowing without prior knowledge, and honestly I still am not sure which answer is the right one.
Clearly the answer has been thought out and decided, since the story of Portal ties in with the rest of Half Life rather subtly and as a rather large retcon, but legitimately and very well executed. There are just way too many signs poiting either one way or the other, so it's impossible to tell.
In any case, I don't really feel like waiting til episode three to find out what the exciting conclusion to this cinematic adventure is. I'll likely stop caring by that time, and have completely lost interest in the game by then. But, I'll never overlook the most important member of the Portal cast: The Weighted Companion Cube. I'll never forget you, dearest object!