Let's see:
- Inspiration, +15% dmg for your group (not ops), lasts 15 seconds, 5 mins CD, requires 30 centering
- Transcendence, +50% speed, 10% defense, lasts 10 seconds, requires 30 centering.
- Some piss healing from watchman (if you're specced into it)
Inspiration is very situational and you can probably use it properly only once per WZ. Transcendence is only good for its speed buff, which can come in handy, but nothing special really. Watchman healing - again, the effect isn't very noticeable. And if you want to deal damage, you should be spending your centering on zen most of the time.
As for the sick damage. Against good groups you'll spend most of your time being CC'd into oblivion. Good players recognize that sentinels/marauders are a threat and CC or focus them. You can interrupt some healing or shutdown a tm spammer for a short period of time.
Sentinels are quite good as node/door defenders. But still worse than stealthers.
Bottom line: the class is pretty fun and performs well in pugs, but in serious pvp it's average.