Here are some of the varied builds/playstyles you can use with each class.
NOTE 1: At level 60, you can max all but one talent tree, and that last talent tree still has rank 4 with 3 points left over. But for the most part, you will only be using 3-4 powers with each class (including bonus power), so 2-3 powers will rarely or never be used.
NOTE 2: I will list the power used, but will only list the evolutions I think matter the most for the build to work
Soldier builds:
Most common Soldier:
Incendiary Ammo: Explosive Burst at rank 6. Recommend squad bonus at rank 4
Adrenaline Rush: All ranks are personal preference, but I think most take Bonus Power at rank 6
Concussive Shot: Amplification at rank 6
Bonus power: Fortification, proximity mine, Energy Drain
Weapons: use whatever you want. Everything works.
* All other powers are just a bonus
Sniper Soldier variant:
Disruptor Ammo: I go for Damage
Adrenaline Rush: I prefer damage and duration
Bonus power: I prefer Fortification for the damage protection and power damage (affects ammo power damage)
Weapon: Kishock (DLC). Can one-shot shielded enemies, guardians through shields without piercing mods
* I also take Incendiary Ammo for max damage (versus armor) and squad cryo for squad
"Bulletless Soldier" (something I have been playing around with the last few days because I was bored):
Incendiary Ammo
Concussive Shot: Amplification at rank 6
Frag Grenades
Bonus power: Energy Drain specced for maximum damage
Weapon: Pistol or SMG with a Power Amplifier mod (Citadel DLC required)
Armor: As much power damage as you can
Playstyle: use only powers to take down enemies.
Engineer builds:
Best Engineer (in my opinion):
Sabotage: Tech Vulnerability at rank 6
Overload: I prefer all damage and Neural Shock; some prefer Chain Overload evolutions
Incinerate: I prefer all damage and armor damage; some prefer radius
Tech Mastery: All power damage
Bonus power: Fortification (durability and power damage) or Defense Matrix (power damage) or AP Ammo (damage)
* All other powers are just a bonus
Drone Master Engineer:
Combat Drone: shields and rockets for damage, OR the other evolutions for more crowd control
Sentry Turret: I prefer Shock, Cryo Ammo, and Flamethrower
Tech Mastery: Drone Mastery at rank 6
Bonus: Defense Drone specced for Radius, damage and radius (because Fire Rate is bugged), Chain Lightning
Puppet Master Engineer:
Combat Drone and/or Sentry Turret
Sabotage: I would still take Tech Vulnerability at rank 6
Bonus power: Dominate (Leviathan DLC), I prefer it specced for vulnerability (not weapon damage)
Multiplayer (MP) Style Engineer:
Overload
Incinerate
Conbat Drone
Bonus: AP Ammo
Adept builds:
Most common Adept:
Singularity (ignore Explosive Singularity at rank 6; not worth it) or Pull
Warp
Throw
Biotic Mastery: go for power damage
Bonus: Warp Ammo or Barrier/Fortification. Some people take Energy Drain
* All other powers are just a bonus
Vanguard Builds:
Most common Charge-NovaGuard:
Incendiary Ammo
Charge: Radius > Weapon Damage > Barrier
Nova: Half Blast and Pierce
Bonus power: Reave or Fortification
Chargless NovaGuard:
Nova: Half Blast and Sustain
Incendiary Ammo
Pull
Shockwave
Bonus: Reave works good. I have seen a guy use Inferno Grenades as well
ME1-style Vanguard:
Pull
Shockwave
Incendiary Ammo
Bonus: Carnage
Weapons: pistol and shotgun only; restricted to Carnifex, Predator, Katana and Scimitar