As you might expect, the Sunreaver Onslaught and Kirin Tor Offensive mirror each other in their collection of a home base on the Isle and their attempts to claim a stronger foothold by sending players (such as yourself) to assault the Zandalari and mogu forces on the island, but they also send you to assail the local saurok as well, which is where I spent most of my time on the Isle.
Upon reaching the saurok region of the isle, I was immediately transformed into a saurok myself via a magical device, which is when I started running around doing what I could. One of the cool things I found were the scattered Cache of the Thunder King chests throughout the saurok part of the zone, containing gold, a vendor grey that sold for between 25 and 35g, and a Lei Shen Ritual Stone.
The interesting bit about the ritual stone is, according to the flavor text, it's a special focus that allows you to summon powerful combatants that will require a group to defeat. Sadly, I had no such group at the time, but it's very interesting. The quests themselves vary from the interestingly weird (like collecting four downed arcane golems, one of which is having an emotional breakdown) to surreptitiously making contact with agents behind the lines.
I also discovered some new lore - apparently the saurok are not buying the mogu party line about their origins, and have found a god to worship... a seven and a half ton tyrant dinosaur god, at that.
There are elite Zandalari to kill, altars to destroy, pterrordax hatchlings to spook, a wide variety of dailies (considering I could only see one days worth for each faction) so I don't expect it will be that difficult to build rep with these factions, especially if they take their lead from the Dominance Offensive/Operation: Shieldwall quests and have story elements periodically as well.
One thing that was really fun to see was the return of old faces. So far, Lor'themar Theron is my candidate for best move into the spotlight of this expansion, and both he and Rommath make appearances here. But as cool as the Sunreavers are, the Kirin Tor sort of steal the show with the return of an old friend.
Yes, the Image of Archmage Vargoth is back, and he's handing out quests. Modera was there, too, but I only had eyes for Vargoth. This time out it clearly seems that the Kirin Tor is fully backing Jaina and the new pro-Alliance direction as fervently as the Sunreavers are supporting the Horde. It definitely looks like both factions will have tons to do on the Isle of the Thunder King, all told.