Krogan Sentinel

Krogan are large bipeds native to the planet Tuchanka, a world known for its harsh environment, scarce resources, and vicious predators. Until the invention of gunpowder, the leading cause of krogan fatalities was "eaten by predators." Though slow, krogan can take tremendous damage in combat, allowing them to inflict grievous harm with impunity.

Armored like a tank--and as slow as one--an angry krogan has more going for it than the species' infamous belligerence. It should come as no surprise that a krogan dishes out as much punishment as they're able to take on the battlefield.

General Notes

 * A popular build for the krogan Sentinel is to ignore Incinerate in order to fully evolve the other four skills. This way the krogan can equip Tech Armor and any heavy weapons he chooses to use without worrying about power recharge time, as Lift Grenade does not have a cooldown.
 * Tech Armour will drastically reduce damage, which becomes even more apparent when using the Rage damage reduction evolutions.
 * They function similarly to the Krogan Soldier with Incinerate replacing Carnage, Lift Grenade over Inferno Grenade, and Tech Armor over Fortification. These abilities make the Sentinel slightly less bulky than the Soldier, but more versatile. Tech Armor provides more damage resistance than Fortification, but does not have an evolution which increases shield regeneration rate.
 * Krogan Sentinels can also be built for a pure melee damage approach. While not as effective as the Krogan Soldier, they don't need to destroy their armor to gain extra benefits. This gives Sentinels a constant level of protection and a large amount of damage in melee to boot, as well as a "panic button" in a tight situation.

Cerberus

 * Lift Grenades are powerful, but only against unprotected enemies. Use it against Phantoms when possible to stop them escaping, or groups of Assault Troopers to deal a good amount of damage.
 * Weaker troops with the right evolutions in melee can be killed outright in just one well placed grenade or melee attack. Be careful if using the latter option as it is risky because of several reasons: you will open yourself up to melee attacks from enemies close to you (which are deadly if they are Phantoms) and a lot of shots from other surrounding foes outside melee range.
 * Phantoms are one of the biggest threats to a Krogan Sentinel, thanks to the krogan lack of maneuverability. However, a melee-optimized krogan in a Rage can kill them with a heavy melee attack even on Silver. If this is unavailable, Phantoms will dodge the first projectile power sent at them, but then usually stand still for a few moments immediately after dodging. So use Incinerate to force one to dodge, and then shoot the Phantom point-blank, or drop a Lift Grenade at your feet then use heavy melee. Tech Armor's detonation also carries enough force to stagger a Phantom on any difficulty, as long as she isn't locked into an animation (such as making a melee attack); make sure you time your detonation carefully or you will be left vulnerable, both by the "omni-tool" animation and by losing the armor's protection layer.
 * Nemeses can often be a frustrating target for a melee-focused Krogan Sentinel, as their quick movement often leads to them avoiding your heavy melee attacks due to the long windup time and equally long finishing lag. Tech Armor's detonation will stagger them, leaving them wide open to a quick kill by a heavy melee.

Collectors

 * Krogan Sentinels will not be effective against enemies with Barriers due to their lack of a real biotic power. Take the Acolyte if you need it, otherwise equip a powerful weapon and make sure if you don't have points in the Grenades, take Incinerate, as you will need it to deal with the armored, or unshielded enemies.
 * Krogan can tank very well due to their rage mode, and will prove particularly deadly once rage mode gets going. Combined with Tech Armor, you can protect yourself from at least 40% damage, 50% if specced out for protection.
 * You really need to watch out for Praetorians since Krogan aren't exactly fast. If the Praetorians get close, they will land at least 2 or 3 hits. While you will take reduced damage, it will still inflict severe injuries, and if you get grabbed, fatal injuries.

Geth

 * Since you don't have to worry too much about powers, you should have an easier time dealing with the Geth Hunters, Primes, and Rocket Troopers, but you should still stick to cover to avoid being constantly stunned.
 * Lift Grenades should wait until you have a group of enemies vulnerable to lifting to avoid wasting grenades.

Reapers

 * Use your Lift Grenades when given half a chance, since they do good damage against any enemy, and lift Cannibals, Husks, and unprotected Marauders.
 * Avoid Banshees at all costs, since you are slower than other races and they can grab you and subsequently instant-kill you.