The Jedi Sentinel is one of the Advanced Class of the Jedi Knight. Its a pure DPS class with 3 DPS Trees.
Watchman specializes in DoT strikes.
Combat specializes in burst damage.
Force specializes in Utility/CC (and is the shared tree with a Jedi Guardian).
The Good: The actual storyline is very good if you enjoy being the goody-two-shoes hero. Thus far (level 23) the bad guys are all interesting and are compelling enough to make you want to continue on with the story. The Dark Side options are not terribly evil, and I could see someone playing their Knight as an "Ends Justify the Means" character.
The DPS is also very nice. When you are allowed to go to town on an enemy you have a lot of ways to maximize DPS and really crank out the damage.
The Bad: While I like playing the story, I do not like the gameplay. The "Focus" resource mechanic feels clunky and out of date. Although you have a couple of ways to build up Focus quickly, the "Ramp Up" time required for several of stances means you can't really unload and kill off entire groups that quickly before taking a fair amount of damage.
Which brings me to my second big complaint, damage mitigation. The Sentinel takes a ton of damage imo. From playing a Trooper at similar level, I was able to kill enemies before they could do much damage. A Sentinel, on the other hand, is required to use his defensive CD's every fight in order to not end below 25% HP. Although you are given a tank in the form of T7, the DPS ramp up time usually means T7 is taking a fair amount of damage (and Kira does more AoE damage to help kill groups quicker).
The Ugly: PvP is terrible as a Sentinel. I say this primarily because a Sentinel lacks any sort of CC at lower levels. Our first CC is given at 24 in the form of a CHANNELED stun. Through talents, some of our abilities can also apply immobilization effects. And while the DPS is great, without reliable CC the class falls behind when compared the Guardian/Juggernauts or Shadows.
Overall: I do plan on finishing this classes story arc, because I really want to see how it unfolds. However, I don't plan on continuing to play the Sentinel class afterwards. There is one caveat. From reading a lot of people say the Sentinel gets REALLY good towards the end. Apparently while some classes get good little by little, the Sentinel gets all of his goodies at the end. This has to do with them being very reliant on Gear and the Top Tiers of their Spec (especially Combat). So I will have to reserve judgment until the end, but right now I don't advise the Sentinel class as it failed to WOW me like the Commando did.