Enhancement and elemental are playable, but you’ll have a hard time ranking with them.
But you’ll definitely struggle more than priests or druids as a healer. PVP: In arena, a resto shaman coupled with a warrior or a ret paladin is very viable with windfury. If you like them in vanilla, you’ll really enjoy tbc. Shamans are one of the most sought after classes in pve. Enhancement is quite demanded, and elemental too due to their utility. Chain heal is just that good, totems too, not much more to say. PVE: restoration shaman is the best healer in tbc pve-wise. PVP: resto druid is one of the top dogs in pvp, with rogues and warriors (in arena): cyclone all the way baby! Overall, your dps specs won’t compete with pure dps specs unfortunately, but you really have a lot of utility so you’re welcome in raids. Balance brings quite a bit of utility in tbc as well, so you’re welcome early on. Resto druid is much better than it was in vanilla too, you won’t feel like a subpar healer anymore. Feral dps once properly played actually has quite some potential…but you’ll have to work way more than other classes with powershifting and stuff. In fact, you’ll be able to be the main tank later on with good gear because bear tank scales really well in tbc. PVE: Rejoice feral and balance druids, you’re viable ! Most raids have one feral druid because of their great ability to offtank and dps with the same spec.
You’re the best duelist in the game and one of the best classes in arena (again, if the patch is 2.4.3) PVP: the monster of pvp IF the patch is 2.4.3. So if you wanted to roll rogue to destroy the dps meters, you may want to think again: only a few people will see that happen. However, only glaive rogues will have a chance to really compete (or even beat) BM hunters and destro locks. Damage starts to catch up in t5, and you’re really good in t6.
Damage early on is nothing to boast about, and your utility in raids is non-existent. PVE: you’re the least demanded class in the game in T4. Fire can see some play but you gotta be really good with it. PVP: frost is not quite as god tier due to resilience and higher hp pool, but it’s still really potent, with more cc (elemental pet), tons of burst and so on. You won’t have tons of them in every raid like in vanilla, but they do have a place with their cc, aoe, good dmg in general yada yada. PVE: although not as good as warlock and hunters, fire mage (and arcane mage during some tiers) does really good dps overall. PVP: sl/sl is a very good pvp spec, but, surprisingly enough, it really gets good later on with gear. Their dps is quite meh in t6 though, but there’s still room for one sometimes due to their utility. Affliction is very good early on and has good utility, you may even see one in raids later on due to that. The gameplay is very boring but you’ll be up there with hunters. PVE: shadowbolt spamming destro = top tier dps in tbc. Shadow priest is ok, and good early on, but melee classes will get better in the latter seasons PVP: discipline priest is a very good pvp spec, almost on par with resto druid depending on the comp (but not quite on average, that’s how op resto was), it’s also a high skillcap spec for those who like that. Holy is not quite as god-tier as resto shaman, but you’re always top tier (right behind them) so you’re in demand for sure. You always need at least one of these guys. Shadow starts out quite strong in t4, and ends up bottom of the pack dps-wise in t6 as dots don’t scale with crit or haste, BUT you’re mandatory because of how insane your utility is. PVE: one of the most interesting classes in pve: shadow is very fun to play, and holy has a big toolkit for tbc. Here’s a little sum-up of what the classes are like, gameplay-wise in TBC: