It depends on what you mean by solo-friendly, Vincire. There is no particular need to join a guild, and much of the content can be mastered solo, if you have patience and learn the tricks of the game. Melee, offensive magic, harvesting and crafting can all be leveled on a solo basis.
Some branches, true, cannot be leveled by oneself.
Healers, for instance. You cannot level healing solo. (It would seem obvious that one cannot learn to heal others by healing oneself.) However, as was mentioned, healers are greatly in demand, and in a small team healing is *easy* to level with the help of a friend or even a chance aquaintance. Once you get to a medium level in healing (say around lvl 100) you can be very useful in larger teams against bosses, even if you can't heal the tanks themselves fast enough, because you can heal the healers very effectively.
((Bosses aren't usually good for leveling, because they take a while to bring down, but boy are they pretty.))
This is a very cooperative game. Even I, who am an old curmudgeon (irl) found myself (eventually) having friends and joining a guild.
Now if by "solo friendly" you mean that the NPC quest-givers can get you the opportunity to be an uber-character ...
Well, in that case, the game isn't even "group friendly."
Come on in and give it a three-week trial.
-- Odo