I've played a Summoner to lvl 11, a mage to lvl 26, a scout to lvl 12, and a paladin to lvl 7.
I've messed around on both league and empire side, and they both have a very stable setup, albeit the league has a slightly easier time for the first 10 levels. The only reason I say that is that their quest progression just flows a little more simpler than empires.
But then again, fuck the league, Empire For Life.
Now, how much like WoW is it?
Id say its just about where WoW was at the end of vanilla when it received the patch for Burning Crusade. If you were not around for that, which I agree was a few years ago, then let me explain the similairities.
It looks kind of like WoW, they both have a history as an RTS before their entrance into the MMO market, they both have a flagging system for pvp, they both have a rich amount of quests and zones, including dungeons(6 are out I believe, which is a large amount for a game still in beta).
Some people are worried about pvp, I personally have enjoyed the Holy Lands so far, and the little pvp i've had. Up to lvl 25 you probably won't even see an opposing faction player. However after that, it will become more common.
Now you don't have to stay flagged, but you do gain an 10% increase to xp for being flagged in an area with open pvp.
So 1-25, 0 pvp, 25-40, about 60-40 pve-pvp.
You don't have to do the pvp, but you will miss out on quests, and every quest you miss is roughly 100 mob kills. So its not worth skipping them to get away from some pvp, and by the time you are 25 you should know enough about your class to stand your ground against most people.
Classes are fairly balanced, although scouts do have an advantage in the Holy Lands due to range and the terrain allowing them to sneak attack people easier. If you do engage in pvp in the Holy Lands then the majority of your pvp deaths will actually occur when you have your flag on and are doing quests and someone ganks you from behind. Personally I've done that to like 7 league players, but i've also had it done to me 10 times from league players

So, after all this hot air, how much is it like WoW? Is the pvp shoved down your throat?
It is similiar enough to WoW for peoiple to easily learn the game without breaking their past MMO experiences, while offering enough difference to create and enjoyable experience that will keep you trying it out, at least casually, for a good long time.
PvP is more prominent than WoW, you go half the level life without any but then it reaches a near 50/50 point of pve quests and pvp quests. If you absolutely abhor pvp then it might bother you, but if you are interested I say give it a chance. The leveling is actually quite enjoyable in this game compared to some others.
And, i'm spent.