Might also want to mention that the Defense, Offense, and Survival amplifiers cost a mere 1000 inf per hour at level 1. So for 24,000 inf you can have eight hours worth of boosts to just about everything if you e-mail yourself the inf before gaining XP.
Generally, that's been enough to let me solo to level 25 or so.
Of the lot, the Water/ set seems to have some of the highest AoE amongst the Sentinel sets.
I paired it with Ice, as the power set had been revised somewhat to where it felt like a completely new set.
The melee and damage multipliers for Sentinels are 0.95. Blasters have 1.125 and Dominators have 0.95 for ranged also.
Anything that summons a pet or a patch uses the pet modifiers rather than these.
Their defensive numbers are at .70, just under the Scrapper's .75.
HP-wise they're identical to Blasters, but they have the Stalker's HP cap.
I've had Vulnerability pop up on targets using the Tier 2 blast.
I've also heard that all Sentinal attacks have a -5% Res and Def debuff, and something about Offensive Opportunity granting a chance to crit for +25% damage.