I have to say, while I'm extremely excited for GW2, I share some of the above concerns about the skill system. Having 5 predetermined skills just seems like such a step back from GW1. It seems like something that will reduce creativity and increase repetitiveness. GW1's system of choosing whichever 8 skills you wanted was pretty good, imo. I really hope my concerns are unfounded though.
Let's take the Warrior for example.
http://wiki.guildwars2.com/wiki/List_of_warrior_skills
From his weapon skills, the last two (Harpoon Gun and Spear) are both aquatic weapons. So counting only everything about that, and ignoring the burst skills as they're a profession mechanic, you have 40 skills to choose from. They come in sets of 2s, 3s, and 5s, sure. But now you have to also weigh the use of each of those skills with whatever else you're carrying. There are a lot of possible combinations, and they're all designed to fit together and accomplish different things; there's no need to always combine that with this for an optimal build. You're then allowed to bring two weapon sets into battle, allowing you to round out your options more.
Now let's look at the skills placed in the second half of his bar. The Warrior has 4 skills to choose for his Heal, 16 to choose for his Utilities, and 3 to choose for his Elite. From those combinations, you have to weigh each of those with each other, and your weapon skills. You don't get to swap in a second set of this in the middle of battle, so their choices are very important. But that doesn't stop you from bring a skill that works better with one weapon set or another, a skill that works for both equally, or a skill that powers your other utilities.
Put that all together, and you're choosing a full bar of 15 skills that work together for you and can answer a number of situations.
Looking back on Guild Wars 1, as a warrior you'd have to bring, let's say, 3 different skills that were specific for your weapon set? And if you swapped weapons in battle, then it had to be for a specific purpose since you'd lose those 3 skills. Then you could fill the rest of your bar with utilities or spells or what-have-you, but at least one slot was going to go for Elites, and in a lot of cases you'd bring a Resurrection Signet as well, right? So that's 5 skill slots used off the bat with 3 slots left, and on top of that you were picking them primarily for one weapon so you if an enemy brought something into battle that countered you, you were pretty boned.
That's the changed philosophy of Guild Wars 2.