Portal 2 is a masterpiece and is as close to perfect as you can get in a game.
SINGLE PLAYER:
Allow me to start off by saying that the best part of Portal 2 is it's writing. The story, the characters, and the dialogue, are so amazingly good, that it amplifies the experience to monumental proportions. The story is so interesting, and cleverly executed. The characters are colorful and hilarious. And the dialogue....THE DIALOGUE!..... is so hilarious and clever. I lost count of how many times I "rolled on the floor laughing." And every word out of a character's metallic mouth is a brilliant one-liner. These three things mesh together to make an experience like no other, and assists in delivering the game's truly unique darkly comic feel. Everything works together so well, even when the dark, creepy, and terrifying side of Portal arises.
The puzzles are so cleverly worked into the story, and they are truly a blast to solve. The difficulty is perfect, it's right in the middle ground, not too hard or easy. Although a many of the puzzles are fairly easy, and can be solved in a few minutes. But this never really poses a problem, as the game never feels too easy. And a majority of the puzzles are right in the middle, with only a few puzzles being very difficult. I was only really stumped once or twice.
Overall, the games looks great. The environments are amazing and complex, and they fit into experience very well. The graphics aren't really jaw-doppingly awesome, but they're pretty good. They're great actually. But not FANTASTIC. Just one level down. If they were better, the game would have been absolutely perfect, but it's a very very minuscule problem that doesn't hinder the experience one bit.
Aside from the graphics, the only other flaw I can mention is that there are loading times in between puzzles. It's not really a big deal at all, it just ruins the immersiveness (?) of the game a tiny bit. Just like the graphics, it's a minuscule problem, and doesn't really ruin the overall experience. Another thing worth mentioning, is that, although Portal 2 retains the dark humor of Portal 1, I found myself a bit disappointed in the difference between the two games in that area. Portal 1 was so creepy, and funny at the same time. Portal 2 still has that same mood, but it's not as dark as Portal 1. But Portal 2 is fifty times as funny. I just wish it had that same bite, that same pitch blackness that made Portal 1 so devastatingly unique. I was a bit wanting in this area, but on it's own, Portal 2 stands up, and then some. I also wish the game was longer. It wasn't really short persay, I just think that the game would have been truly epic if it were longer. Depending on your skills as a puzzle-solver, it'd take you probably between 7-12 hours. It's satisfying for the most part, but I would have loved it if they added 30 or so more puzzles to it. The game truly would have been perfect.
Overall, the single player campaign, is simply magical. It's so much fun to play, and is so entertaining and engaging on so many levels. I'm very picky with my games, and I get very easily frustrated and annoyed, and with almost every single game I have, I've had at least one major complaint, but I can't really say that this game has any serious flaws. All the aforementioned are barely even worth mentioning. I'd give it a 9.9 if I could, but a 10 suits the game well. I haven't finished co-op yet, i can't really say the game is perfect, but from where I'm standing, it's looking that way.
CO-OPERATIVE PLAY
Co-op was a refreshing re-imagining to the Portal gameplay formula, by adding another element to it: another player, and two more portals. And it plays beautifully. Portal takes advantage at this opportunity by providing the gamer with very clever and ingenius uses of the cooperative mechanic and the puzzles work brilliantly. The only problem is that a great majority of the puzzles are too easy. Me and my brother breezed through most of the puzzles with no sweat, but they were still fun to solve, and it was still amazing to behold the complexity and intelligence that is in Portal's co-op gameplay. There were still several puzzles that were very difficult and had us stumped, and there were some that had the middle ground difficulty that most of the single player campaign had. The writing isn't also as entertaining as the single player's as GLaDOS is your only source of material. She has a few funny quips but I wasn't laughing as hard as I was during Single Player. I also felt that co-op was too short. Well, I wouldn't really say it's too short, I guess I just wish it was longer. As the whole thing goes by pretty fast. The same I could say about the Single Player. They are both about the same length, although I think the Single Player is a few hours or so longer. Co-op has around 36 levels, but as I said, many of them can be done in 5 minutes. So, depending upon yours and your buddy's puzzle solving skills, I'd say it's about 5-7 hours.
All in all, Portal 2 is a glorious gem of a game. It's mind-blowing in every sense of the word, and it just hits it straight in the chest like no other game. The bottom line is that Portal 2 is fun, it's brilliant, it's laugh-your-ass-off funny, and it's just a unbelievably good game. BUY IT.