I've tried a few of them and they seem a mixed bag. Mostly talking from a WvW perspective here.
Rev's is stupid strong, like 53k on the dummy and going to get severely beaten by the nerf bat strong. The kit is a bit awkward though- the AoE of the 5 is really a bit too small to be usable in any situation where there's lag, though, so blob fights are right out. It could be an OK replacement for M/A in a pure condi build, but I think you'll still wind up mostly on SB anyway. For a cele build it will have trouble displacing either the range and area denial of SB or the mobility of GS.
Ranger's is a really fun, slippery kit with a lot of snares, and all the stealth is very silly with Relic of the Unseen Invasion (600 range AoE superspeed for 2s on stealth). Downside is that the damage just isn't there for it to be a threat.
Warrior's is solid, great upgrade from rifle for a ranged kit. Still some issues with lag and it's all projectiles so it ain't it for blobs, but I could see it seeing some use in a roaming kit. Tough to give up the sustain of staff or the mobility of GS, though.
Necro is really just sword with a different coat of paint and more to manage. I like the idea of it as a ganking / engage-and-burst option, but I've had the 2 dodged enough times now to be grouchy about having that much of the damage bound up in a single ability. I could see it being useful to land the 4, precast either the 5 or CttB, then port on and swap to shroud to finish the burst.