Hmmm, not even sure where to start. Been playing WoW for years, after researching extensively and actually checking out Wrath(beta) I decided it was time to move on, I honestly wouldn't be playing WAR now if it wasn't for Wrath redefining suckage from my perspective.
I had two main toons, my mage which was my first and by far the most time into(around 150 days played) and my drood with a ton less(around 40 days played, maybe less, haven't checked in a while). These two gave me a good chance to really appreciate how profoundly bad Blizzard is at balancing classes. Mages got slammed constantly with a nerf bat, even when it was clear they were way behind everyone else- Blizz game up with a dmg tax on them... shocking how lopsided it was. OTOH you had droods, retardedly OP in both PvE and PvP and pretty much were given huge buffs in every patch and with every piece of new gear(just check their pvp gear vs priests, droods get way more mp5- which they need even less then priests, and don't pay any penalty for it). Played through most of the Tier6 content(and through the T4/T5 blah, blah, earned my bear mount etc) Just a bit of a side tangent, just framing things so you can understant my current PoV on WoW
First off, not entirely sure what the last poster was talking about but WAR isn't remotely close to WoW in terms of PvP. The general idea between how you get into a BG may be close, but that's about it. All of WoW's characters were built around PvE first and foremost. PvP was a tragic afterthought which as of now is just plain embarassing. WAR, OTOH, was built entirely around PvP and it shows- both in PvE and PvP. This profoundly changes the game mechanics, the equal of a prot warrior in WAR has TONS of utility in PvP- straight PvP mind you, not just for tanking Van/Drek The Chosen class, one of Dests main tanking classes, has an ability called Guard, I can pop that on you if you are say a healer and absorb 30% of the dmg you would take(that gets real nasty if it's another tank say, carrying a flag and I pop it on him ), another talent called hold the line where I reduce every friendly targets dmg taken by ~15% as long as they are behind me. These are just fairly simple examples, just trying to point out the general theme that runs throughout WAR- everyone, every spec is viable in PvP.
You mentioned how much you love grinding( ) WAR will probably let you down there. If you die? Yep, they took out that painful walk back to your corpse- no more grinding out gold for repairs either, not in the game, all you get is a debuff you can pay off(normally about the cost of killing any random mob your level) or wait 15 minutes and it will go away(10% reduction in hp, it does stack though ). Grinding to level? Not likely to be needed, if you are willing to do a bit of traveling(which is MUCH faster then it is in WoW) you will outpace the quests for most of your playing time(before doing all the Tier2 quests for each of the three zones, you will be well into Tier3). It isn't like I have gotten to play around with end game yet, but so far grinding is pretty much non existant in the game at all.
Instances are FAR less frequent then they are in WoW, but PQs(Public Quests) honestly make it so I don't miss them. You don't even have to be in a group- just show up and if a group is already working on it, you just help them out and as long as you contribute you get to roll on the loot- without ever having to be in their group(these reset quickly). Loot drops are a bit better setup then WoW too. You roll on bags of loot, inside the bag will normally have a couple of good items and some random junk- you get to chose one item for yourself. There will ALWAYS be something you can use in the bag(by that I mean equip, I suppose it is possible that you may already have the item in the bag at which point you could take one of the other randoms or the money).
The RvR in WAR is actually really enjoyable(far more so then the instanced PvP IMO). Each zone you enter has a certain segment that is flagged for open PvP, inside these zones there will be objectives you want to tak to gain control of the area. Sieges on keeps have been a blast so far, you have to batter down the gates, fight off the guards(NPCs) while dealing with the opposing faction. You can enter and leave these zones at will, participating in them or the other type of PvP will gain you renown points which level up much like normal leveling(you also gain XP from PvP kills). Renown levels don't go away like the old ranking in WoW if you were playing then, but they give you access to the same types of rewards the old PvP system in WoW did. Unlike that system, a constant grind isn't necessary, just play when you can and you will level up your renown at your own pace. Another element that is nice about the RvR or PvP system, if you jump in to a BG or RvR zone at level one it will promote you to level eight to give you a fighting chance(your stats will be adjusted up to go along with this). Not quite the same as actually having the level as you won't have the new talents etc, but it won't be like walking into WSG at level 10 and getting one shotted over and over by that twink from the opposing faction(heh, doesn't even really need to be all that twinked for that matter with a 9 level difference). Also, this game pretty much eliminates twinks as you see them in WoW, because you gain XP in BGs you won't be having to deal with obscenely OP toons as you do in WoW.
Oh yeah, back to the grinding element. You get your mount at level 20. By the time you get to that level if you are relatively frugal with your money(which there is no reason not to be honestly) you will likely have double the amount of gold you need for it. Nothing like WoW where you could spend a week or more grinding out the gold to get your basic transportation. Also, respecs so far are incredibly cheap, so if you were a spec akin to a destro lock and wanted to respec back and forth for PvE/PvP it would be a nominal amount at best, nothing like the 50G a pop that WoW charges you for frequent respecs. This isn't likely to be an issue though as from everything I have seen every spec is viable in WAR period, although specs do seem to make much less of a difference on your toon overall.
Another thing I like about WAR. You train a talent once. Rank15 Shadowbolt? No, there is one rank, and every time you level up it gets more powerful. At some point you may get 2 talents for one level, but from what I have seen so far you get one new talent with each level. This may not sound like much at first, but considering you are never buying new ranks of anything and you get it every level it actually feels like more then WoW has by the time you get into your 20s. Also seems to be less lame duck talents then in WoW, some you will certainly use more then others, but I have yet to get one and think 'when the hell am I ever going to use this'.
So far I am absolutely loving WAR. Maybe Blizz will fire a certain egocentric developer and fix what they are doing in Wrath and make it so WoW would be appealing to me again, but even if they do at this point I wouldn't drop WAR. Too much to like about this game right now. Maybe when I get to end game and see what they have to offer my tune will change, but I am having an absolute blast with it so far.