Vindictus feels faster, more fluid and more action packed. The environments appeal to me more as well and it feels like skill plays a bigger role. Visually, TERA feels more "polished" and will probably have more content, but the gameplay itself isn't particularly exceptional. It's good, but not great. There's also something about it that doesn't feel nearly as satisfying. I can't quite put my finger on it, but it has to do with the bosses. It almost feels like it works in a very formulaic, stereotypical manner like many other MMORPGs. It lacks the same kind of excitement.
Thus far, I definitely have to agree Vindi is faster paced, and thus, skill is more obvious. The bosses seemed too easy to me due to the large lag-time between the obvious tell and the attack, but the lvl 22 instance sped things up and the lvl 27 was probably the most fun I've had in an mmo for a long time.
The giant enemy crab-like thing pretty much did as he pleased. To see the tell, you had to actually pay attention, and if you didn't dodge/block you could count on a swift death. He had 8+ attacks and could stop in the middle of them if he saw an opportunity to smack someone. Tanks (Be it Lancer, Warrior, or w/e) aren't gifted with hax aggro generation either so everyone had to constantly be on their toes.
I was told the game didn't get hard until ~ lvl 20-30, so I'm looking forward to what else is in store.