Alyx might get a little annoying, but at least she can shoot better than some people you'll meet in deathmatch.
The game takes off right where half-life 2 left off, and takes an odd turn almost immediately. Gordon and Alyx are whisked away to safety with little explainable reason, while the G-man is kept at bay in much the same way and never shows up for the rest of the storyline. In the same vein, Eli and Mossman-- the two other doctors from Half-Life 2-- are introduced and quickly forgotten in the midst of various Combine attacks on their respective areas. The 'advancement' of the story is mainly just introducing new questions and not answering them, but this is forgivable, considering how fun the game still is. It goes to note, however, that much of the game has been injected with a lot more obvious humor. For example, Doctor Kleiner (the fumbling, bald scientist) now occupies the screens and televisions blurting out various forms of propoganda instead of Breen. In his speech, he makes little 'side-notes' to begin procreating to increase the human population since the Combine suppression field for preventing such things, itself, has been surpressed. Some jokes fall flat, completely on purpose; when first encountering a 'Zombine' (a head-crab infected Combine soldier) Alyx cracks the joke about a Zombine, coining the term, and then shaking her head at her own lack of good humor when the ever-silent Gordan doesn't even chuckle.
As far as graphics, gameplay, and even sound, much of it is unchanged. This isn't really a bad thing, however, since all these resources have not simply been re-hashed; the new locales and interactions with the environments actually feel kind of refreshing, though some of them are the same old tricks you saw Valve pull previously. Electrified water with barnicles, numerous headcrab traps, and air-ducts galore (which Alyx actually cracks jokes about as she follows you). The shooting and puzzle solving is done in such a way it's never really boring, and many of the puzzles involving the gravity gun are done early on and not revisited. Most of the other puzzles are environmental traps mingled with combat, as you'd expect.
As far as Valve's overall goal of 'character and story development' goes, Gordon doesn't get much (which isn't a surprise), and to be truthful, nor does Alyx. In half-life 2, she's a bad-ass that doesn't talk too much aside from very important plot points. In half-life 2, she's still a bad-ass, but it's peppered with odd and almost uncharacteristic fits of sadness, mourning, or even simple fear. At one point she'll be curled up in fright after a train crash, but the key point is that it's NOT the crash that scared her-- it's the mostly harmless 'stalkers' that serve as workers for the combine, getting in her face. Through roughly 90% of the game, Alyx tags along interjecting both important points and sometimes complete nonsense ( Example: "I heard that whenever Dr. Kleiner locked himself in his office, you and Barney would race to see who could get inside without a key."). It's not really an escort mission, since she seems almost invincible through most areas, absorbing explosions and gunfire, and there are even some special animations such as kneeing headcrab zombies in the groin and so on. The problem is, she may actually start to wear on your nerves after a while. She states obvious answers to puzzles, such as "In my experience with electricity, they're always attached to a power source." Some sections may come off as annoying, but she can hold her own, and for the first section of the game you're only armed with the gravity gun and instead rely on her for your covering fire. When poorly armed int he dark against all those zombies, you may not have enough ammo to fight back; Alyx has a limitless supply, but she needs light to fire accurately. Putting a flashlight beam on zombies is an interesting mini-game, to say the least.
Combat plays out just like in Half-Life 2, only for the first sections of the game you are very poorly armed and instead get help from Alyx. The combat is still pretty intense and purely action-movie quality, from defending yourself from an onslaught of zombies in the dark, to blasting gunships with rockets in a rickety wooden building that splinters apart as the machine tries to get a bead on you. The problem is that, by the end of the game, you really wanted to continue onward and fight off some more of the Combine and whatever they could throw at you. This is where Episode 1 shines; the environments are still quite dangerous and interesting, such as a head-crab infested hospital, the dark matter core ( a puzzle area), and so on. However, there seemed to be a much bigger emphasis on the zombies than any other enemies; you only see the white-armored combine a couple times, and they are easily dealt with and easily forgotten, for example. The important fights of the game, however, are riddled with some fights you'd expect, but still manage to feel intense and exciting.
It also goes to note that a number of technical problems managed to filter their way into my system, but this may be unique to me. There were loading problems, occasionally freezing from time to time, and at one point Alyx was stuck in a key area and I couldn't progress until I loaded the game from scratch and completed the area over again. This didn't seem common, as the second time was smooth as silk and the problems didn't really slow me down.
All in all it is more of the same, which is exactly what Valve promised. Alyx may get on your nerves, if you're like me, but it's forgivable considering just how much she makes up for it in defending herself; she's certainly no princess as far as manners go. For 20 dollars, it's a good buy, even if there are no new weapons and only one new enemy.