The Sentinel is a highly tactical, fun and rewarding class which extends gameplay beyond the repeated use of guns and highlights many of the unique aspects of Mass Effect's combat system.
The Sentinel, in many ways, plays the opposite role of the Solider. The Sentinel rarely relies on her guns, but instead focuses almost exclusively on both biotic and tech powers. No other class offers the same ability as the Sentinel to strip defenses from hostile targets, making it powerful on the battlefield for its ability to "soften up" targets to a point where they are easily dispatched by her squad.
To define the Sentinel, we first should define what it is not. The Sentinel is typically not a "front line" class. Bonus Powers notwithstanding, the Sentinel does not come equipped with any ammo powers to increase weapon damage or direct damage powers such as Incinerate, Charge, Slam or Combat Drone.
Instead, the abilities of the Sentinel are designed exclusively for removing the defenses of targets and controlling the battlefield (and do little against health). Warp and Overload strip barriers, armor and shields, while Throw and Cryo Blast offer an element of crowd control. Tech Armor exists largely to increase the Sentinels basic survivability, as her ability to kill targets independently is diminished compared to other classes.
The Sentinel, therefore, typically keeps herself at a safe distance. It is less important for a Sentinel to reach advantageous positions for gunplay, and her use of weapons is limited compared to other direct damage classes. However, because the Sentinel is so capable of removing the many defenses targets come equipped with on Insanity, it is often the go-to class for higher levels of difficultly. Do not underestimate the Sentinels ability to leave targets wide open for an easy kill.
During combat, the Sentinel will often stay behind cover, utilizing her powers to remove defenses as often as possible. Cryo Blast can be very useful in preventing targets from getting too close - as without any true direct damage powers, targets which reach her position can only be dispatched with her (comparatively) underpowered weapons.
Controlling squad mates becomes significantly more important for a Sentinel. Because Sentinels are often not the class delivering the "killer shot", she will rely heavily on her squad mates ability to reach good positions for aiming down the battlefield. She must be constantly aware of their position at all times relative to the enemy, as losing a squad mate as a Sentinel can be much more devastating compared to other classes.
At the beginning of combat, the Sentinel should position her squad and immediately identify the enemies defensive mechanisms. She should attempt to use the appropriate power as soon as possible - both to begin her cooldown and to maximize the benefit from potential "area" effects on her powers. Powers should be used immediately as they become available to maximize her effectiveness. Gunplay during cooldowns is acceptable, but leaving enough shield to survive the next power use is vital. Tech Armor has a very long cooldown, and needing to deploy it during combat dramatically reduces her effectiveness.
Pausing the action by using the radial menu is critical to the success of a Sentinel. A high level Sentinel will have more than 2 powers available, potentially upwards of 4 or 5. Choosing the right power for the right target and squad positioning all benefit from the pause offered by bringing up the radial menu. Shortcut keys should be used sparingly, if ever.
Taking the right squad members is important for a Sentinel, but perhaps less so than most other classes. Since there is not a single defense layer which she is unable to remove herself, the Sentinel has an increased flexibility to choosing her squad mates. The Sentinel is therefore an ideal class for experiencing the combat and dialog from a wide range of available squad mates.
Perhaps uniquely to the Sentinel, Mirada is one character that, while necessary for most other classes, is least valuable to the Sentinel. Miranda herself is loosely based on the Sentinel class, thus her character is designed to fill a niche the Sentinel more than adequately fulfills. Instead, the option becomes available for the Sentinel to bring more focused and specialized squad mates for each mission.
It is often quite beneficial for the Sentinel to choose one squad mate which comes with an ammo power, specific for the mission, or one which generally increases the damage done against armor and health. Overload easily removes a full shield from most all enemies, even on Insanity difficulty. Warp quickly removes barriers, and while it does have an increased effectiveness against armor, armor tends to take longer to remove. Squad mates with Incendiary, Shredder or Armor Piercing ammo dramatically increase the squads ability to finish off the targets the Sentinel has softened for them.
The Sentinel is a unique class which offers a powerful, yet indirect, means of dispatching enemies. It is highly favored for higher level difficulties where Tech Armor plays a vital role in survivability, and where every enemy comes with at least one form of defense which requires removal. The Sentinel is a highly tactical, fun and rewarding class which extends gameplay beyond the repeated use of guns and highlights many of the unique aspects of Mass Effect's combat system.