Mass Effect 2 guides here:
List of Strategy Guides Found on the Forum compiled by Pacifen. (Some links may no longer work; I have updated it here).
Most of the guides deal with Insanity difficulty.
Best bonus powers for the Sentinel;
- Stasis
- Energy Drain (for shield regen + shield damage)
- Reave (for armor and barrier damage + health regen)
- Warp Ammo or AP Ammo
Personally, I recommend 1-point Stasis.
Your Sentinel essentially reaches its peak with this build:
1 - Throw
0 - Warp
4 - Assault Armor
0 - Overload
0 - Cryo Blast
4 - Guardian
1 - Bonus power
From there, you can put points into whatever you want. You can prioritize the build in one of two ways:
1. First max Tech Armor to Assault Armor, then max Power Mastery to Guardian.
2. First max Power Mastery to Guardian, then max Tech Armor to Assault Armor.
Either way, with a level 50+ import, you should be able to get both maxed before Horizon.
Remember, powers and weapons can deal bonus damage to protection layers (shields, armor, barriers). List in this thread.
Enemies completely frozen by Cryo Blast or lifted by Pull take +100% weapon damage, so Mordin and Jack are good squadmates.
Defense-stripping squadmates are also good with the Sentinel as they can strip protections quickly for you. For example, Garrus, Mordin, and Miranda are good squadmates.
Sentinel Tech Armor detonation (when blown off by enemies) can damage and knock down enemies, so getting in close enough so enemies can be hurt and knocked down is a good strategy. It may require some practice at first, but you can get the hang of it.
About Tech Armor evolutions (Power Armor versus Assault Armor):
- Power Armor gives you +100% shields, but when blown off only leaves you with health.
- Assault Armor gives you +75% shields, but when blown off gives you +50 shields. Essentially, +125% shields. Also, increases radius of detonation.
You can make any bonus weapon work, but I prefer shotguns on the Sentinel. Run into enemies, Tech armor gets blown off, shoot a bit with the shotgun, reapply Tech Armor. Take cover if you need to. Repeat. Shuriken is a good shotgun replacement early game until you get your bonus weapon.
I think starting at rank 3, Tech Armor gives a hidden (unintended) bonus of resetting squadmate cooldowns. So you can use squadmate powers, have your tech armor blown off, reapply tech armor, use squadmate powers again.