Wasted potential and too short.
It seems that the developers thought the MP would compensate for it's short SP time, but it does not. It falls short with it's small amount of main missions and side missions, which aren't too varied. They could have added a bunch of side missions to compensate for the short main plot, but did not.
The weapon choices aren't too balanced, so in the end you will likely only look at 3 or 4 weapons and never use or look at any of the others. Strangely, you pay to upgrade your plane for black market weapons, and they turn out to be worthless compared to the SC weapons, which will likely be the only weapons you use once you have the credit to upgrade. Having a wide array of non-lethal and lethal gadgets, short to medium to long range weapons(including sniper rifles), and suppressed and un-suppressed weapons, gives the player a nice selection to choose from and lets them decide how they want to approach situations for the most part. The custom load-out slots are useless in SP with their reduced gadget count, and is likely something you will only use in SP.
The addition of the personal mini-drone is nice and allows you to scout out the area ahead a bit. The over-watch sections vary the gameplay nicely and help focus attention on your world and the story, instead of constantly reminding you that your job is to just sneak around in a man-suit.
Apparently your flight crew is too minor for you to interact with. Even when one gets injured and is sent to the infirmary, where: he mysteriously cannot be found! Apparently he is either Snake (Metal Gear Solid), or he is invisible.
Giving players the ability to interact with the flight crew, and have face-to-face chats with Sarah over the net would have added an additional layer of depth to the story, but again, is something Ubisoft chose to not take advantage of. You are sometimes given the option to knockout an important character or kill them after an interrogation, but regardless of what you decide, you will always get the information you need, and the decision will not affect the story- it has no weight; Ubisoft dropped the ball again with it's wasted potential.
Overall, the story is solidly written an the ending leaves it open to a sequel being produced in the near future, but not allowing you to decide what to do with the final boss once he's defeated, might leave you a bit upset when they gave you that choice with other characters all throughout the game.
You won't really run into any glitches, this has been well tested, but you will occasionally open and close doors instead of turning off lights or climbing walls, which frustratingly, will lead you to killing yourself when Sam decides to have a mental-retard moment and play "Open-and-close the door," in front of a patrolling guard.
Overall a solid experience, but not enough to make this a stellar experience.