The Protector Trials isn't a must have add-on, but if you're craving more Bioshock 2 action, this should fit the bill.
The story is pretty minimal at best here. Brigid Tenenbaum has tasked you, another, though identical Big Daddy to weaken the ADAM supply of The Family by protecting the Little sisters as they gather the precious material from dead bodies. Thats about all there is unfortunantly, which is a bit odd given Bioshocks very story driven nature. Thankfully its not a real let down for the whole package.
There are 6 stages here, each based on a re-done location from the campaign. Each stage has 3 waves(trials) of splicers each, for a total of 18 trials. All you must do is to protect the Little Sister until the end with as little Splicers getting to her as possible. To do this, you must strategically you all the traps, weapons, and plasmids you have at your disposal. The catch? Each trial only gives you an already choosen set of equipment. This is done to force you out of your safe-zone, forcing you to use some of the less useful weapons to your advantage. Sometimes the equipment gives you an advantage, such as Electro-bolt on a stage filled with water. Other times, you will get only a set good for setting traps.
As I played through each trial, I experienced some of the most fun and frustrating moments I've ever experienced in the game. It really pushed my expertise of Plasmids and Guns to the limit.
As complete trials, you earn a score based on how much your sister was interuppted as she worked, and you will recieve an amount of stars just for finishing. As you collect stars, yhe game rewards you with some really cool bonus loot like early artwork, pre-release footage and ideas, and some other exclusive stuff Bioshock hardcores can devour. There is also 7 new achivements/trophies to strive for included, however they are all pretty easy to get, but are still neccessary if you're aiming for 100% completion.
Sadly, there is not a whole lot of replay value here. of course, you could always aim for a better score in a trial you fell behind in, but chances are you will probably ace them all the first time around.
Thankfully, this add on can be bought for a very reasonable price of $5 on the PSN. It doesn't break the bank at all, and you get a few hours of splicer killing goodness. Bioshock junkies should give it a try. Its a cheap, fun way to prove your the true king of Rapture.