Great potential, but ultimately a let-down.
First of all, the most important part of any game, the actual GAME PLAY, is broken. Most engagements in MGO break down into simple spray-'n'-pray style gun fights, requiring little actual ability, further hampered by the ridiculously easy head shot system. This causes most other attempts at combat to be hopeless endeavors; CQC results in painful deaths from afar, and snipers are easily shot down at range by those with faster firing weapons. The cover system, useless when trying to actually take cover while firing, and the difficulties of weapon selection further hamper the game play. All of this leads to games filled with camping gunslingers constantly spraying at head height, ruining what could have been a well flowing match.
One aspect of the game that is well-realized and very promising: the skill system. It allows for a lot of customization in terms of your own style of play(or, it would, were it not for bad mechanics inhibiting use of anything but fire arms). Of course, this, in and of itself, isn't extremely innovative and original, but that isn't a bad thing, and it succeeds at expanding the package.
The map selection is very poor, though this can be remedied through expansions, the sign-up to actually play online is infamously dreadful, and limiting each console to one character seems rather extreme(talk about unneeded micro transaction).
All in all, the main problem with this game is that tactical espionage action simply doesn't translate well into online play, involving real players in real time, especially because of the lack of real available stealth system.