In general, mostly balanced. There are some hard-counters, but nothing ever occurred to me as OP.
In PvP, what separates a good and bad player is skill. Knowledge of his spec, limitations an forces, and also knowledge of the enemy's spec. In WvW gear does matter however, as you're using PvE gear there and you should be lvl 80 if you want to be at your best. GW2 may have less skills that some MMOs, yes, but it also plays a lot on dodges and active defenses. Your traits, runes and sigils choices are also very important.
To me there is no overplayed class. Pretty balanced. Sometimes you see a bit more of a particular class, but nothing worth worrying about imo.
I play necro in PvP, and I hate warriors. I play using fears, immobilizations, chill, enemy boon->condition conversion to control my opponent and keep him away from me while my conditions eat away his health. But warriors have nice abilities to overcome these conditions, and they tend to have a lot of knockdowns and the like. Necros have very few defenses against those. Never played your games so can't give you a comparison.
Crafting is important for ascended armors and weapons, and also legendaries. For the rest, you're better off buying your armors from dungeon vendors or from the trading post.
Armor type function mostly like in other MMOs, as in heavy armor will give you more armor that light stuff.
I always found GW2's pvp a bit lackluster in terms of what you can play. I'm more of a PvE person so I might be biased, but there's not many different game types in PvP. Basically capture points. There's one map for deathmatch, and the new PvP map seems very interesting, but I would have loved more diversity in game types.
I've never been a fanatic of PvP so I can't tell if GW2 will suit your needs. But at the current price, I'm sure you'll at least get your money's worth.