tl;dr: Gameplay is solid and suprisingly good with a reasonable amount of depth. However, the grind from lowest level to max level (even with someone grinding you) can be nigh unbearable. The games optimization is hit-or-miss with many players computers as the optimization seems to be based on CPU power with it hardly if at all utilizing the GPU. In terms of class-to-class balance, the actual devs are fairly incompetent at making sure one class doesn't completely dominate the others.
The gameplay of Dragon-nest is primarily fast-paced combat with heavy reliance on reflexes, ability to predict the enemy movements, and knowing your own skills. The combat has no casting bars rather relying on animations which makes you feel as though you are 'in control'. Many of the higher level skills do a satisfying amount of damage in PvE and a reasonable amount in PvP. In my experience, the end-game content (Dragon nests) often devolve DPS races to blow up the boss before it has a chance to do any of it's harder mechanics. Simply getting hit by some of these bosses could result in an instant death for you. Note: In the end-game content, after you die, you are dead until the raid (called 'nest' ingame) is complete or your entire party dies.
PVP deserves it's own section because for many players it is simply all that matters in the game. PVP is largely player-skill based as a highly skilled player can easily combo the other player to death, giving the other player no opportunities to fight back. There are a few types of PVP in Dragon Nest which I will describe quite simply. There is Ladder, Endless, 1v1, and blacklisted 1v1.
Ladder is what many players might call 'competitive' mode with a rating, but in reality, it is simply an infestation of a single class. Gear plays a role in this mode and for many PVP'ers, no one actually cares about it, since gauging it as a metric of skill is completely stupid.
Endless is simply 8v8 combat. Given its playercount, it is easily the laggiest mode for many players and, simply put, is a mind-less cesspool of high AOE skill-spamming. Gear does not matter.
1v1 is what it is. Gear does not matter.
Blacklisted 1v1 is different from what you might expect it to be. To give it a bit of a background, many players view some skills as overpowered compared to other skills (example: A mercenary's 'Iron Skin'). Most classes have a few of these skills and players will mutally agree to not use these skills. For some players, Blacklisted 1v1 might include entire classes or very specific rulesets and for many players, what is blacklisted to someone might not be blacklisted to the other. Most 'legitimate PVP'ers' play this.
One other 'important' aspect about PVP is PVP rank. PVP rank is arguably important because there is an icon associated with your rank. Initially, it is a brown egg icon next to your name. As you PVP more, you get more experience and the icon changes. The other icons are blue (silver) and yellow (gold). However, be warned, the blue and yellow icons are EXTREMELY difficult to attain as they are exclusive to a certain rising XP threshold. It is difficult to describe in words but simply put, if you were to attempt to become the player with the #1 amount of experience, it would easily take you a year of pvp'ing to get even close to it.
The sounds of Dragon Nest are fairly average I would personally say, although, one of the key issues many players seem to have is that the voice-actors for some of the classes are borderline cringeworthy, prompting some users to completely disable the voice or download a foriegn language voice mod. Another one of the issues and to many players and advantage is that most if not all the skills have their own special voice-line for casting that spell. This means when your Adept (that's a class) casts Inject, every single time you are going to hear what sounds like a child say, "This might sting a bit!"
The graphics are good and fantastic for many of the skills. However, some classes and raids (nests) in particular have crippling effects on many player's computers. One class in particular, the Alchemist, has a few spells that are strong in PvP simply because for many players, casting it is 'like opening six movies at the exact same time', resulting in a crippling half-second burst of lag.
The community of Dragon Nest is fairly odd. A mix of Anime fanatics and normal people coupled with a loud creepy population. The population seems to be a mix of 12 to 19 year olds with some guilds greatly skewing this margin. I highly recommend finding a guild that suits your playstyle rather than joining one of the ones that you get invited to right off the bat. The best way to do that is make a friend in-game and try their guild.
Server & Game Issues:
The server occasionally seems to have frustrating issues with lag. Sometimes these issues are extremely frustrating as they might completely void and entire 'nest', leading to a player missing out on loot. One of the most notable issues is the completely unavoidable 'Hackshield', and instant kick from the game resulting in the failure of the games anti-cheat. It is not detecting a false-positive, merely it just messes up.
Suprisingly, this game isn't nearly as pay to win as I expected. The only pay-2-win'ish factor seems to be Dragon eggs and, even then, the only good thing that comes from them is wings which boost your characters movement speed in everything but PVP. When it comes to costumes, 'green' costumes boost stats which can pretty much only be purchased through NX (real life money). However, 'blue' costumes which boost stats much greater than 'green' costumes can only be reliably purchased through large amounts of ingame gold.
Overall: The game is suprisingly good but has a good few problems that detract from some of the good parts. The game seems to have a large issue when it comes to grinding of either money or levels. There are minor issues with the community regarding it's vocal immature side.