So, my Lancer advanced a bit more (I didn't have the time to hit the OBT cap of 32) and I'm fairly confident that Tera will offer good PvP. Granted, I only have experience with 1 of the 8 classes, but some of my fears of melee vs. ranged were assuaged as I gained new skills and glyphs. For example, the Lancer has an ability where he tosses a spirit chain at his target and pulls them back to his location (Mortal Kombat Scorpion style), then you can immediately Shield Bash (stun) and work your damage combos. The Lancer also has a Frost Nova that slows rather than binds, but it's still a somewhat effective cripple. I chose to Glyph my Charge to increase my in-combat speed by 100% for 7s, which definitely helps chase down enemies trying to kite. While it's not perfectly balanced, I'm satisfied with my PvP options. Lancer and Berserker can also block spells with their block mechanic. Slayer and Warrior, conversely, have a dodge mechanic to dodge spells (harder to master, but adds mobility where block does not).
Griefing is VERY viable in TERA, and it can be quite fun. There are many escort quests that allow you to camp out by the destination and turn on your PvP flag to kill the person trying to complete the quest, forcing him to start over and some escorts take 10 minutes or so. Since the game is new, there's often streams of people doing the same quest at the same time offering several targets back to back. Also, currently you can add ANYONE to your friends list since there are no factions, which further allows you to track down anyone you might want to kill until they realize what you're doing and they remove you from the list and toggle the "do not allow people to add me" option, which isn't on by default. You can camp people across multiple zones as they try to teleport and flee, at least until they wise up about how you're gaming the system.
Guild v. Guild wars are also interesting. It's somewhat like the old Order vs. Chaos part of UO. It allows you to kill anyone, anywhere (except in major hub cities), including new players on the newbie Island of Dawn without flagging to the rest of the populace. There were situations were low levels were leaving their guild over the weekend because level 32s were trolling level 5s on the Island of Dawn.
PvE:
I also ran the first dungeon available, which is built for level 20-25 characters. Similar to the rest of the PvE it was pretty dull. Every fight is tank and spank, the only difference is you don't just stand there like in WoW, you have to dodge attacks manually and use your block/dodge key to mitigate direct attacks. I guess its better than WoW, but the simplicity of the mechanics was a turn off. Of course, I'm sure as the game goes on they will introduce more complex fights and the "action combat system" is marginally better than most other MMOs I've played (WoW, SWTOR, Lineage 2, Shadowbane) in that it requires more focus on your positioning and such.
Bottomline, if you decide to dive into TERA, be ready for a much longer grind than prior MMOs. In the time it took me to hit 24 over the weekend I'd probably already be max level in SWTOR (by comparison) and the max level in TERA will eventually be 60. Also, you'll basically be playing it to PvP all the time, but they aren't releasing the battlegrounds and rated system for the US server on release (though it does exist on the Korean servers so it probably won't take too long to implement). The game has its gratifying moments in that justice is meted out by the players themselves--someone tags the boss mob you were waiting for, just flag and beat their ass (and you can talk shit to them too since there's no factions). But, it lacked any PvE to make the grind somewhat enjoyable and PvPing in the open world without any real penalty to the target (escort griefing notwithstanding) has some limitations.
If only they would remake old school UO with the TERA engine...