First things first:
Everyone is max level in pvp. You automatically get upped to lv 80, and in sPvP you automatically get a full set of lv 80 pvp gear. Weapons, armor, amulets and runes can be 'bought' freely from the first npc's, so everyone is equal in terms of level and gear. You spend your pvp points (glory) only on better looking gear, but they'll have the same stats.
Now, sPvP:
Structured pvp is pretty damn awesome. It's not a zerg fest unless of course you go 1v3 or something. Classes are pretty well balanced, though some are maybe a bit stronger than others. Survivability is good too, so you won't see much 'I hardly had time to react before I died' moments. It usually takes 10 sec or more, at it's fastest to kill someone. More often than not a fight 1on1 can last over a minute. Each class also has a lot of different 'specs' to go with.
Take just the thief for instance. (my main) I could go pure condition damage, doing most of my damage with bleeds. Or I could go for direct damage. Or I could go for support, using traps and tricks to aid my team with cripples, blinds, short stealths, etc. Or I could even go vitality (hp) and toughness (defense) to make a kind-of-tank. (real tanks don't exist in the game.) Each of those roles can also be played as either ranged (dual pistols, pistol dagger or shortbow) or melee (dual dagger, dagger pistol or sword dagger) So yea, 12 different 'main' play styles just for the thief already, with even further customization possible. (For instance toughness + power for good direct dmg, good defence, but hardly any crits.)
WvW:
World versus world is a bit different. You do get upped to level 80, but your gear stays the same as your PvE level. As in, you can be a lv 80 running around in lv 2 gear in WvW. Not super effective, but you can do it. As for the fights, it's mostly just one big zerg. Either you overpower the team defending with numbers, they overpower you with numbers, or you happen to come across a place that's not defended. Real strategic fights aren't a thing yet. But that will surely also come with siege weapons and once WvW becomes the real 2-week-long thing instead of a daily thing, and people figure out some tactics.