As Pirates of the Burning Sea nears its release date (22nd of January), and the servers are already online for those who pre-ordered, the impressions I gained while participating in the open beta that ran for part of December (GamersGlobal reported) might be of interest to those who have not yet decided whether to purchase the game or not.
It should be noted, though, that I only played as a naval officer, my knowledge of the other classes stems merely from observation.

Overview
The game is set in the Caribbean of the year 1720, during the so-called Golden Age of Piracy (although a balanced distribution of the factions has taken precedence over historical accuracy). Players can choose between four careers for their character, namely naval officer, privateer, freetrader and - of course - pirate. The first three can be played as a member of either the British, French, or Spanish nation, while the pirates form the fourth faction. Quests and battles are completely instanced.

Character Creation
On character creation, you can choose from a variety of faces, hairstyles, garments and accessories (but only an astonishingly small number of eyepatches), so you can start your character's life both as a realistically dressed trader, or as a Jack Sparrow-lookalike. The clothing is color-customizable (you can wear all pink if you so wish), can be changed in the game by visiting a tailor, and you can earn new clothing through quests.

Leveling
Said quests are the main way of gaining experience, going out on your own to battle NPCs is not nearly as profitable. As there are no actual stats (like stamina, strength, etc.) that you can modify, the main way of improving your character is by buying larger ships (which always have a required player level). Additionally, you receive one skill point per level. First one for naval skills, then for swashbuckling, then naval skills again, and so forth. These skills have a huge impact on combat. As a naval officer, for instance, you can learn skills that raise your ship's defenses (at the expense of speed), or even make it invincible for a few seconds. Pirates, on the other hand, have a variety of skills that increase the repair rate of their ship's, or can even throw their cannon overboard to increase speed, if outnumbered and outgunned.

Economy
I can't say all that much here, because I was much too occupied with firing broadsides (and too impatient with all the text) to finish the tutorial quest on economy. However, I can say this much: Basically everything that you can purchase in the game is created by other players. NPCs merely sell civilian versions of ships, that have only one point of durability, that is they only have one "life". Player-made ships usually have three durability, meaning you can let your ship be sunk three times before you lose it. Items are sold in a regional auction house, but if your freight lies in a different port than the one in which you bought it, you have to sail there and fetch it. Even in the beta, with the number of players being relatively low, the system worked fairly well. I always found one or two deeds to the next best ship when I had saved enough money to afford it.

Swashbuckling
Swashbuckling, i.e. melee combat, is the part of the game that still needs the most work. There has been a patch since the end of the beta, but I doubt that it addressed all the open issues. Most of the swashbuckling quests send you through the same forest (or warehouse, depending on the quest), with groups of enemies in the same locations. Now that could be excused, if the fighting system worked properly. Most of the time, you either walk through hordes of enemies completely unscathed, or you barely manage to scratch the first NPC before you drop dead. There are also those quests where you get rushed by 20+ enemies on entering the area, but I'm guessing (hoping?) those were bugged in the beta and have been fixed.
Anyway, if you die, all is not lost. You may still resurrect yourself with smelling salts, and you get a bunch of those for the first few quests. Once those are gone, however you may want to cut back on the swashbuckling missions to save the salts for story missions, as one unit of smelling salts cost up to 500 gold in the beta - that's 1/20th of the price of the first ship that is worth buying.

Ship To Ship Combat
... is great. Period. The amount of fun you can have hunting enemy merchant convoys is unbelievable, and it increases exponentially with the number of cannon your ship has. That said, the placement of ships upon entering a battle is somewhat strange. If you are part of a group, and one member begins combat, you all spawn more or less the same way you were distributed before combat - so if the group stays closely together, the enemy has a problem. If you enter someone else's battle, however, the position you spawn in is not all that logical. I once entered battle between an enemy ship of the line and an enemy frigate, maybe 50 yards apart, one of them facing my bow and the other my stern, only to have another hostile frigate spawn astern. Survival was, obviously, not an option. This was luckily an exception, not the rule.

Quests
While the swashbuckling quests aren't all that good (and rather dull), the naval quests are quite fun, and range from escorting ships over patrol duty to mere "destroy all enemies" missions. The group missions in particular are entertaining, due to the sheer mass of hostiles thrown at you.
Apart from that, there are also a number of solo quests. These are mainly normal quests that you do on your own, telling a story and advancing you in your chosen career. There are also times when you simply have to walk from one NPC to the other and hear what they have to say, but those are rare enough to not get on ones nerves.

Conclusion
To sum up, one can say that PotBS is a game with great potential, but also with a number of rough edges that still need polishing. Another month or so in development wouldn't have gone amiss, but if you like the scenario, want a change from World of WarCraft, and are willing to pay the monthly fees (practically identical to those of WoW), then you should definitively consider giving that level 1 light corvette a spin.