¶ Summary
The Sentinel sees little use in PvE combat. In PvP, it can be an effective solo hunter against small prey, able to immobilise a target and slowly chew it to pieces using its drones. Unlike the Curse and Pilgrim, it has no stealth capability, so opponents will see it coming. It is also a very effective small gang PvP ship, able to serve as a powerful force multiplier. For weapon disruption pure and simple, though, the Crucifier is a better choice, as it has bonuses to range as well as strength, and costs a fraction of the Sentinel's price.
¶ Skills
Electronic Attack Ships should be trained to level IV before undocking the ship. The bonuses attached to the EAS skill for the Sentinel are massive—e.g. 80% extra neutralizer range per level—and since this is consistent across some comparable ships too (such as the very useful Keres and Hyena), it can be worth training the skill to level V in the medium or long term.
¶ Tactics
In solo PvP, the Sentinel usually kites, trying to stay within disruptor range but outside of scrambler range. It begins fights slowly, as its neutralizers will take a little time to drain the target and as its DPS output is anaemic. Provided the Sentinel can survive until its target's capacitor is dry, it can usually achieve full range control. The solo Sentinel's engagement options focus on other small ships and on highly capacitor-dependent ships (ironically including many Amarr hulls); ships with numerous and/or bonused drones, with a capacitor booster, or with zero-capacitor weapons (projectile guns and missiles) will stand a much better chance of driving it off. It is hard for a Sentinel to lock down several enemies at once, and it cannot go all-in on an isolated target by overheating hull-mounted weapons, so groups will be a difficult problem even if they are split up.
In small gang PvP the Sentinel's job can be simpler: identifying threats on grid and shutting them down. It can kill off capacitor-dependent DPS, and it can also contribute to screening, because neutralizers can make opposing tacklers dead in the water, albeit not quite as instantly as a scram or web will.