Send in the clones!
The gameplay itself doesn't have a whole lot going for it. Combat is pretty dull and requires no skill - your main attack is automatic and your only strategy involves firing off spells/skills as they recharge. Party combat is simple as well - keep your tanks up front and focus all the party members' attacks on one monster at a time. Once you get the basic premise of it, combat has very little variance or surprises - it's simply a matter of using the same spells in the same order and watching your opponents' hit points steadily drop to zero then on to the next one.
The quests generally involve moving from one end to the other end of a map, requiring you to clear out pretty much all the monsters in the area as their aggro is high and the paths are narrow. There are also optional quests which offer skill rewards - killing boss monsters, freeing prisoners, putting out signal fires, etc. Because of the instancing the world lacks the continuity and change-ability of most MMORPGs (Guild Wars is not an MMORPG in my book). Once you leave a zone and re-enter, everything resets to its original state... same monsters in the same positions, etc. The city/town hubs are basically waiting rooms for the next mission where people buy/sell stuff and form groups. Forming groups with other people can be a crap-shoot. If you end up with even one moron in your party, the whole mission will probably be lost, as I've seen people aggro huge mobs on purpose. The NPC party members are decent although always under-leveled compared to real players, and the AI is pretty crappy, especially the healers.
Character customization is highly overrated. There is one prototype for each class gender, so basically everyone ends up looking like clones of each other, just in varying heights, skin/eye colors.
The magic items are terrible in this game, very generic and underpowered, even at the highest level. Wow, I have a gold wand that increases my fire magic recharge rate by 20%. The 'fancy' armor, like the stuff in the Citadel or the Grove may look nicer than Drokknar's, but it offers no additional protection, and it costs an insane amount of resources. So after you've finished the main quest and most of the side quests, your primary objective in SP will be gathering the 80 million resources needed to assemble Fissure armor. No thanks.
I tried the PvP a few times. Not too great.
Strangely, while I was playing Guild Wars, I found it somewhat addictive, though not very enjoyable. From start to finish, the SP campaign should take at least 150 hours to complete, so you do get many hours of play per dollar. It has been a long, long time since I last logged into my account, and frankly I have no desire to pick this game up again even with the new release of Factions.