Metal Gear Online is a great game, and definately a great addition to the Metal Gear Solid series. This is a must play..
This is a great game that every person should play, Metal Gear Solid fan or not. THe gameplay is very good, and is mostly similar to that of Metal Gear Solid 4's gameplay. Graphics are very good, as well as the leveling up system and skills.
There are a number of different kinds of skills that you can select, which over time increasingly get better with new abilities like slitting someones throat. You can also by doing well in the game, get reward points and buy new clothing items and accessories in the reword shop. There are also a number of different game modes; from Team Deathmatch to Team Sneaking. There are also gamemodes where you can be Snake and Otacon's Metal Gear. These different game modes are also quite fun.
All and all this game is a very good multiplayer and is still growing, with new levels and playable characters and expansions being released every few months. Overall you must play this game, especially for the Metal Gear Solid fans.