So, I'll just speak from the Enhancement side of it. Having played Enhancement for many years on retail as well as 3 times on Vanilla.
Oh, my. If you ask me - You are in for one hell of a ride. Well, that is, if you go Enhancement.
But ye be warned. Not many people want anything to do with an enhancement in their raids (except for the single one using
Nightfall). However you can always opt to just PvP with it. Enhancement is THE one-shot class/build in all of Vanilla, if you ask me.
(Although in late parts of Vanilla, Warriors tend to get so crazy with the item scaling, that their burst in PvP can sometimes outperform even WF)
You have to understand that, Shamans can't dual-wield in Vanilla, that was something introduced in BC - So, to compensate for the massive DPS buff that is dual-wielding, they also had to massively nerf the dmg you get on a WF proc, and normalize the proc rate with a psuedo-random mechanic. Similar to what DotA uses on some of its' heroes.
Of course that change in BC, changed Enhancement forever, and made it an actual "sort of" viable dps spec in raids. And it definitely got some talents and new kinks that helped enhancement be taken more seriously in the PvE aspect of the game.
HOWEVER - The vanilla Enhancement used 2handers, which you gain through the talent tree. And proc'ing WF with a 2hander in vanilla... Let me tell you.. It's something to behold. Especially when you get the proper weapon with the slow swing speed and decent gear.
Things don't really get rolling however as Enhancement until you get Stormstrike, at the bottom of the Enhancement tree. The skill might seem a bit lackluster at first glance, with such a long cooldown holding it back for any real PvE dps purpose. However, just the fact that it gives you another instant swing - That is the cake on its' own. Getting a chance to proc more WF more often, is all you want in life, baby!
So once you get Stormstrike, a decent weapon and gear, and as a must bonus: Hand of Justice. - Then you'll have a fun time 1 shotting anything in your path PvP wise and solo PvE / 5-man dungeon wise when WF procs.
Or even better, when the stars align, and you proc WF on the normal swing + on the Stormstrike + on the HoJ.
That's 1+2, 1+2, 1+2 = 9 instant swings (6 of them being WF hits, with massively increased Attack Power - the bonus hits from WF always hit way harder than the normal one). - Then factor in your crit chance - And you'll be making swift corpses out of just about anything with 5k HP or less.
But I digress, I'm rambling now about Enhancement PvP... Of course they're great fun there, but their PvE side, is a typical hybrid story. You'll do less competitive dps than the proper dps classes, and relying 100% on a 20% proc chance as ~75% of your damage output or more? - Well, let's just say you're the least consistent dps in the game. - But you'll still pull aggro every now and then on mobs if your first swing is a WF proc. Trust me, that's not so fun, haha.
As for Elemental and Resto? - Eh, about the same deal as ever. But then again, I never play healer, and the only played Elemental in BC and later. And the only difference in Vanilla Elemental compared to later - There's no Overload mechanic, so you won't see as many billions of lightning bolts, aww. - The dps is less, so again, not a competitive dps spec. - Decent for PvP, when you have Elemental Mastery ready. Otherwise, elemental is a pretty meh spec. - It's alright for leveling, though.
Wouldn't know anything about resto, like I said, never heal.
Probably the most famous vid regarding the topic:
https://www.youtube.com/watch?v=ja1j7xWpB3w#t=20And here's another bonus one:
https://www.youtube.com/watch?v=pbAD6RqOUJo#t=69