Little is known about the batarianhomeworld of Khar'shan or its inhabitants. As a result, the race is judged by those whom the Hegemony allows to travel beyond its borders: organized crime enforcers, pirate boarding parties, slaver gangs, and gladiatorial combatants.
Batarians are large brawlers that use nets and spiked weapons to capture targets... or to bleed them dry on the battlefield. If an opponent gets too close, a batarian enforcer bludgeons them with spiked armor and enforcement gauntlets.
As the name might imply, the Batarian Brawler Vanguard excels in melee combat as a skill build. In particular, his long build-up but unmatched melee synergizes flawlessly with Biotic Charge: by starting the heavy melee right after the charge sequence begins, he can be at the point of impact with a stacked damage reduction right out of a charge, essentially meaning he can 'brawl' enemies with a one-two of the Charge-Heavy.
With his powers properly evolved, the Batarian Brawler can easily achieve over 100% damage reduction, combining the stacked bonuses from heavy melee, Blade Armor and Biotic Charge.
With the right timing, when following up a heavy melee on a unprotected target (just health) that has been launched far after a Charge, the Brawler will literally slide along the ground until reaching the target and successfully hitting him with the punch.
The Batarian Vanguard lacks virtually any direct damage in his abilities except for Biotic Charge, and is therefore not suited to go toe-to-toe with bigger, tougher foes like Praetorians or Atlas Mechs. Take a powerful but light weapon, such as the N7 Piranha and equip it with a Shotgun High Caliber Barrel. This will allow you to deal with more powerful foes.
Lash will stop most of the smaller foes from being able to fight you, but will prove worthless against armored units.
Lash can, however, set up detonations for Biotic Charge against unarmored units.
Blade Armor should ideally be maxed out, specced for protection and reflect damage. This will make the Brawler much more difficult to kill.
A moderately light loadout is highly recommended, to keep Biotic Charge cooldowns fairly low while maintaining weapon dominance between charges. Or, if you want to spec yourself for melee damage, take a light shotgun (such as the N7 Piranha) or a close-combat heavy pistol (such as the M-358 Talon) with melee mods in order to maximize lethality in hand-to-hand combat.
Lash will be most useful here, since all enemies except for Dragoons and Atlases can be affected by Lash. It can stagger Atlases, but that's all it will do and inflicts no significant damage on said mechs.
Blade Armor will also be effective here, since you will be charging into enemies more often than not, and the Phantoms and Dragoons' main proficiency is in close quarters. While it can also be used on Atlases, their massive shield and armor levels will make it nearly impossible for a reflect strategy to work against them.
Be careful against Phantoms, as charging into them will leave you vulnerable due to the nature of physics vs enemy melee attacks. Regardless of whether you have Blade Armor on, they will be able to follow up their spin melee attack with an impalement that you will not recover from.
However, Biotic Charge will always stun Phantoms, allowing to successfully follow up with a heavy melee before a Phantom's counter-attack. Just be extra careful to not charge into a group with more than one Phantom.
Also, the heavy melee will hit Phantoms even while cloaked, since the attack locks onto enemies.
Be careful against turrets. However, if you have a light loadout, you will be able to go toe-to-toe with a turret, as the turret cannot significantly damage you while in the heavy melee animation. Take advantage of this by alternating Biotic Charge and heavy melee.
Your Biotics will serve little use here, since only 3 enemies are susceptible to Lash: Troopers, Captains, and Abominations. Lash is even less useful when used against Possessed Abominations, as their explosive power and radius can seriously damage you and your squad, or even kill all of you outright on higher difficulties.
Blade Armor is useful against Praetorians since their claw attacks come in hard and fast, but their protection leaves an issue. Furthermore, it is no good if you end up getting grabbed and subsequently killed as you cannot reflect damage if one instantly kills you.
Every enemy has some form of Barrier, except for Scions, Abominations and Troopers when unpossessed. Some form of protection stripping, such as the Acolyte or weapons with Disruptor/Warp Ammo, will deal with this problem.
If thrown in the right direction, Lash can reveal Geth Hunters even if the aiming reticule is not available.
If the Rank 5 (Damage over Time) is taken, the constant damage will expose the cloaked Hunter.
Blade Armor will help immensely against Hunters, since they will sometimes sneak up on you and melee you in the back. This will stagger them, and give you enough time to either counter-attack or flee.
None of the Geth can instantly kill you, so all you need to worry about is making sure you don't put yourself in a situation you won't be able to get out of. Remember, Geth Rocket Troopers, Hunters, Primes, and Bombers can stun you with their attacks; therefore you should plan your attack and assess the situation, before you literally go charging in.
Heavy melee can hit Geth Bombers even during their high, bomb-dropping flights. Just make sure to start the attack before they deploy.
Every enemy (except troopers) has at least some form of shielding, and therefore some method of shield stripping, (such as the Acolyte) is advised to destroy their shields and leave them exposed to Lash, or the biotics of teammates.
Do not charge into Banshees. As with all bulkier classes, batarians cannot roll; this will spell your doom if you charge said enemies, since you won't be able to immediately pull back like nimbler classes can. Every other foe is game-- for Banshees, steer clear.
However, though ill-advised, one can charge when a Banshee is approaching with biotic jumps, since she will not use any attacks during them, and a charge will land where she started the jump rather than where she jumped to. This places you at a relatively safe distance behind the Banshee.
Lash will benefit less from the Penetration evolution, and will generally be less useful since only 3 enemies can be affected: Husks, Cannibals, and Marauders. Consider one of the other powers instead of Lash.
Blade Armor is rather effective versus Brutes, as all of their attacks are melee-oriented. Be careful, though, as your health and shields are, as always, in finite supply and it is ill-advised to take on several brutes at once.