I'm only level 14 on my Engineer, but will give you some key points that keep me playing it instead of anything else.
- Warhammer lore > all others IMO
- Each race-class has a somewhat unique feel. It's much nicer than having the same exact class between every race and faction.
- Very polished from the start. For those of us that remember WoW from 2004, there is no comparison.
- This game is built around PvP, not PvE. You can gain EXP and level up through PvP in both open world or scenarios. You can still level through PvE and see the story if you wish.
- Siege warfare. Took my first keep with a warband at level 13. This type of gameplay element is like crack.
- Some of the best base line UI customizability.
- Built for group PvP, not the solo-fest some other games are.
- The world is more 'alive' and you feel as though you are part of it. Faction control of certain areas plays a huge part in this.
- Your level plays a bigger part of how you compare in combat.
- Auto-ranking feature if you enter a scenario (battleground) as a low level. You can start playing these as soon as you create your toon at level 1. For Tier 1 (covers from ranks 1-11), you will be auto-adjusted to 8. Tier 2 makes you 18, etc. This buffs your stats and abilities to level 18 equal. Ranks = levels BTW.
- Add-on community is already alive and kicking. Check Curse Gaming.
- A database site is also kicking. Wardb.com
- Mediocre game performance which is sure to be addressed.
- Somewhat laggy in busy situations. I'm sure this will be addressed too. It hasn't prevented me from doing things and having a blast.
- Kinda slim itemization. Gear is based upon class, and sometimes race, more than anything else. No generic plate, chain, or leather to choose from.
- Huge faction imbalance overall. Compared to WoW, it's the polar opposite ratio of Order-Destruction (vs Alliance-Horde). WAR's Destruction = WoW's Alliance. Hopefully this will be addressed with transfers and server mergers.
That's all I can think of right now. Overall, it is top-notch in my book. I haven't had this much fun in an MMO since WoW pre-TBC.