There are 5 quest items you need to farm to enter Thornmarch. The first time you go you feel like just farming the pop items is harder than Ifrit. However, once everyone knows what their are doing and how everything there aggros and such, it won't really be a huge deal.
First off, Guardian of the Grove:
We don't want to know what we did to piss those trees off... but they will mess you up unless you tiptoe past them. Oh and don't aggro anything else near them or they will 1 shot you...
So pass a ton of those plus wolves and raptors and you can get to the NMs needed:
Queen Gougou is pretty easy, just don't let her tempt you off the bridge. Also good to note, there are 2 bridges and 2 Queen Gougou.... This little fact confused the crap out of us last night.
The great oak has some exciting moves but if you can stay out of aoe range and have the DD kill from the side you should be ok with a good tank. (We had the BEST tank) /em blushes.
The hog does that pushback thing but its not all that hard. NOTE: see that Scout Vulture? We didn't and if it aggros under the trees you die.
Yucky aoe but still not all that hard. Once you figure out how to fight without moving and aggroing the trees, you should be fine.
Don't ever look into a Spriggens eyes O.o
Seriously, it's easy.
All of that for 5 items and then you chat with a cute little moogle and get to do this:
I don't have a whole lot to say about the fight as we only tried it a couple times and then people started logging off. The CS is cute.
One other thing to keep in mind is that there will be a lot of other linkshells there, and instead of fighting over the NM's, helping each other is a better plan. Since the pop items are a 100% drop, and the NM's have an extremely fast respawn rate, things will go much more quickly and smoothly for everyone involved if you just team up. Help take down the NM, or clear out the vultures or spriggans that are distracting. Everyone will be happier this way.
As an added bonus, have a song: