I played Tera until a little before the brawler patch, I got the "master of time & space" title and dropped the game completely as a main PvE'er I felt I had nothing more to do. I loved the combat, I mained Lancer and its the most fun I've had in a game for a long time. Dungeons in Tera is where the game shines, very good fights with plenty of great mechanics, they keep everyone on their toes atleast until you overgear stuff, I think BnS doesnt give you that experience. That feeling you get when you kill Darkan HM, yeah not sure, I have yet to experience this in BnS but I honestly have faith it will happen.
I will admit I'm a BnS noob since I just started to play on CBT2, but my impressions of the game were very good right with Blade-Soul Gold, I played only KFM to 45 and Assassin to 23, other classes in the 15 ish'es.
Started as an Assassin and man was I having fun, the combat requires precise timing, and a sequences of skills gives you sometimes different results than other sequences of skills, it makes you feel like youre playing a fighting game instead of an MMO. This was new to me, the combat was fast, required skill, and it punishes you if you dont perform correctly, I'm not using the word "punish" in a negative light btw, I actually love this.
My second class was a Kung Fu Master, I actually dropped my Assassin at 23 because I though well, I should try other stuff, and I loved KFM instantly, KFM is a VERY punishing class when it comes to ping and timings, but its so rewarding when you land things just in time. I use to hate PvP but that changed in this game, yeah I suck, but I have so much fun with KFM that it doesnt matter.
BnS follows several staple formulas used in MMO's, Questing, gear grind, etc. But the combat is SO GOOD, that it doesnt matter, if you get some Blade And Soul Power leveling. It carries the whole game.
TLDR: Tera and BnS similarities end with them being both MMO's from korean devs, BnS combat is so good it carries the game. I prefer BnS I', having so much fun.
Edit: By the way what I meant with no RNG costumes was, theres no RNG boxes in the store that you buy for the chance of a costume akin to gambling