Now, to be honest, in th time I played Moonkin, the gameplay didn't change that much. Of course there where some spells lost (like Insect Swarm) and some spells added, but the gameplay didn't change much. You had this eclipse bar which moved left/right when casting either Starfire or Wrath. And now Blizzard seems to be changing that.
On other characters I already know how that feels. Going from TBC to WotLK, the complete gameplay of tankadins was changed. Most notably going from Spellpower to Strength gear. There where also a gazillion spellchanges. Going into Cataclysm they added Holy Power, which was one of the main reasons I actually stopped playing Paladin for a while.
I also had a lot of problems with hunters after they lost mana, and gained focus. You get so used to a certain gameplay, that heavy changes really hurt your joy when playing a character. I still have troubles using all the bigger cooldowns on my hunters, they have a lot of them.
Last week, Blizzard released the new Alpha patch notes, with lots of changes for the Moonkin. If you want to read them, go Google it, or visit the patchnotes somehwere. I am not going into a lengthy rant about them. What I did have was a gut-feeling that I don't like them. There is something amiss it seems, and it took me 5 days to actually find what I didn't like.
The problem is two-fold. The first one is that all DoT's will become 'fluid'. At this moment DoT's are 'snapshotting' the stats when being cast, and keep that for their whole duration. In WoD, the DoT's will look at your stats everytime they tick..... except the Moonkins eclipse-bonus, that is still a snapshot. Which means you still want to cast Moonfire/Sunfire at the highest amount of eclipse possible.
The other factor is the new eclipse-bar. At this moment it is moved by casting spells, in WoD it will move automatically on a 30 second interval. That means you no longer have control over the eclipsebar, it just keeps moving while you are in combat. And there is the problem, your spells have the biggest oomph when eclipse is high, same as now, so what's the problem? Well let's look at the start of (almost) every fight I do (It starts around 1 sec before pull);
Pot-Starfall-Wrath (to hit lunar)-Sunfire-Treant-Moonfire-4 time Starfire-Starfall-Starfire-Celestial Alignment-Moonfire-Starfirex3-Starfall-Treants in between, and always Starsurging and... now the problem is movement here. If I have to move in that first 45 seconds of the fight, it will be a huge dps-loss.
Luckily most fight have a fairly static beginning, but now imagine having a big cool down every 15 seconds...that activates automatically, and you have only a 4.5 second window to cast the big spells. That's how I see the new eclipse-system. If for whatever reason you have to move during that top-eclipse-phase, you will loose a lot of dps.
Now, we don't know what kind off fights we will have in WoD, they may be more static then now, but the fact that RNG can heavily influence boomkin-dps seems silly. And that's I see the system.... which may not be implemented. Maybe it will actually work.. but we need to wait for that.