I adore the skill system in GW2. It's diverse and elegant, with lots of choice and restrictions to make it very interesting.
You have a limited number of ability slots. Only about nine or so. The first five slots depend on the weapons you have equipped. Each class has a different set of abilities for the different weapon types they can equip. Slots 1 to 3 come from the main-hand weapon. Slots 4-5 are provided by the off-hand. A 2H weapon gives all five slots. Slot 1 is an auto-attack.
As an example, my Guardian can use swords or maces, along with shields and off-hands. A sword gives more offensive abilities, while the mace is more defensive. The shield gives protective abilities, while the off-hand leans more towards healing.
So changing weapons means something, it actually changes your gameplay. It's not just cosmetic. This also allows GW2 to make weapons feel appropriate. The sword is all slashing finesse, while the 2H mace is slow and hard-hitting.
Slot 6 is a healing spell. There are four or so different spells you can unlock, but you can only choose one at a time.
Slots 7-9 are extra abilities. You unlock them with skill points that you get as you level, and you can use any three.
The Guardian has a lot of abilities which have both a passive and active component, including abilities that you can activate to give friendly players around you a buff.
There's also traits, which are virtues for your class that you can invest in and they give bonuses to specific stats. For example, traits for the Guardian include Honor and Zeal. Very Lord of the Rings Online, in fact.
I really like the skill system in GW2. It's structured, but also has a lot of options. Weapon choice means something.
I'm not certain if the observations in this section are Guardian-only, or if they apply to all the classes.
The combat in GW2 is ... odd. At first glance it looks like standard MMO combat, but it really isn't. There's no resource involved, so ability use is governed entirely by cooldowns and the situation. But it doesn't seem like there are enough abilities to form what we would traditionally think of as a "rotation". In particular, GW2 seems enamoured of medium-term cooldowns at the expense of short-cd rotation mainstays.
Now, my thinking on this might be skewed because I'm coming from a SWTOR marksman sniper, which features a very formal A-F-X-X rotation with something like 9 regular abilities. (It's actually a little excessive, and I actually want to write a post about it sometime.)
But GW2 combat is like having a paladin with auto-attack, Crusader Strike, and 6 abilities that each have a 1 minute cooldown and are highly situational.
So what does actual gameplay end up like? You start auto-attack, and hit Crusader Strike on cooldown. Maybe use a cooldown every so often, but those abilities can only be used once per fight, and you'll maybe use only 1 or 2 of them.
Now, maybe this is better in PvP, where it could become all about moving and timing those medium-term cooldowns.
But mundane PvE is a little boring, with lots of waiting around for the next ability to come off cooldown. I find myself gravitating to the weapons that have abilities with shorter cooldowns, just so I have more buttons to press.
So far, crafting is pretty similar to crafting in other MMOs. I just want to mention something that I thought came *this* close to amazing, but GW2 didn't take that last step.
Among your inventory is a "collection", which is a grid of every single crafting material in the game. You can send crafting mats directly to your collection from your backpack. This is huge for preserving bag space and organizing crafting mats. I really like the collection, and hope that more games steal it.
Unfortunately, when actually crafting things, the game does not look at your collection to see if you have enough mats. It only looks at your backpack. So you have to move mats from your collection to your backpack before crafting.
You can see how much more streamlined crafting would be if the crafting UI could draw directly upon the materials in your collection. They're so close, and they just didn't take that last step.