These two spells helped build the new foundation for shamans going forward in Wrath. Lava Burst helped change the way Elemental works (by being able to change the way the class procs its clearcasting and other on critical abilities) and Hex was (and can be argued still is) the long-await Shaman CC ability. We discussed shamans in PvP last week in the upcoming patch 3.1, and I think it's safe to say that both of these abilities (especially Lava Burst) helped prod the class into its new directions, along with the enhancement specific Maelstrom Weapon.
When Lava Burst first debuted on the beta for Wrath, it almost immediately caught the attention of both enhancement and elemental shamans with its ability to guarantee a critical hit combined with Flame Shock and its use as an instant cast with Maelstrom Weapon. Eventually, MW was changed so that it didn't work with Lava Burst, making the spell primarily a way for Elemental Shamans to guarantee a crit and for any shaman out soloing to get around the ridiculous drop in offensive capacity all shamans (especially elemental and restoration, as enhancement shamans can at least still hit them) face against certain nature-immune mobs.
Lava Burst was the first step in moving shamans into a much more mixed damage mode of play. While nature damage is still very important with Lightning Bolt and Chain Lightning and numerous talents that support them, Lava Burst means that shamans now have a reliable way to deal fire damage as well as a way to ensure that if a critical hit is needed to proc a talent such as Elemental Focus or Elemental Devastation, the shaman no longer has to wait and hope. Thanks to the cast time, enhancement is much less likely to try and work this spell into a rotation, but it can serve as an effective opening cast on a boss to get the critical hit train rolling, so to speak, and for elemental it basically means that stacking crit is no longer as important as spell power or hit rating, since any effect that requires a crit can be has with a mere FS/Lava Burst combination.
Honestly, Lava Burst is a good spell, a very efficient spell, and the addition of the Shamanism talent in patch 3.0.8 made it even better for caster DPS. If for no other reason than its lessening of our reliance on nature damage, it would be a worthy acquisition when you hit level 75. But combined with the synergy it displays with other talents and spells, it becomes very nice indeed.
When Hex was first announced I'm sure all shamans were very excited. Finally, shamans get a form of CC for PvP and instances! Sure, we'd have to wait for level 80 to use it, but that was at least in time for heroics and arena play.
Hex has ended up being a pretty solid form of CC in PvE content. Mobs you cast Hex on do not attack you just as the spell description says, they hop around like frogs. You can leave them hexed and run away, you can deal damage (unlike Polymorph, the effect doesn't automatically break while you're attacking the hexed target, meaning that if you can get lucky you can kill a hexed mob without taking any damage at all) and in an instance if you hex a mob he'll generally flop around for the 30 seconds, making it very viable as CC.
The only real dificulty here is that nobody waits for CC anymore, but that's not the fault of the ability. Hex would have been simply marvelous for shamans looking to run instances during The Burning Crusade, and to my mind is one of the clearest examples of an ability designed for the expansion we just left (similar to the old principle that armies are almost always prepared for the last war they fought instead of the one they're about to fight) but since it's a level 80 ability, you don't really get to use it when leveling through the new content. If I had one wish it would be for Hex to be lowered in level so that shamans would get more use out of it when soloing and grinding XP to level up.
However, the pros and cons of Hex in PvE aside, it's generally been considered somewhat of a weak spell in PvP. For starters, a hexed PC can continue to move at you, meaning that it doesn't really help a shaman get out of range of melee who are trying to kill him or her. Frankly, Frost Shock works better for this than Hex does. Since Hex might not break on damage, you can use Hex then Frost Shock to remove your attacker's ability to hurt you then hope you can snare him or her without breaking the hex, but it's still clunky and inelegant. Secondly, Hex is easily trinketable, which makes it interesting.
Effectively, in PvP Hex functions as a combined disarm/silence effect. Now, a disarm and silence effect would be a very powerful PvP tool except that, unlike other disarms and silences, which cannot be removed as easily (I'm sure there's ways to remove them that I'm forgetting at the moment) Hex can be removed with a simple trinket or racial that "Removes all movement impairing effects and all effects which cause loss of control of your character"
This would be reasonable if Hex actually impaired movement or caused you to lose control of your character. But it doesn't. You can still move while hexed, and you can still control your character while hexed, the only thing you can't do is attack or cast spells, so it's a disarm/silence (admittedly, a real disarm still allows you to make unarmed attacks which Hex does not) that can be removed, unlike Dismantle or Silence. Hex is effectively neither fish nor fowl in PvP and suffers for it.
Having said that, it's certainly not a bad spell. It's just not as good as we all hoped it would be. It's a solid PvE spell that doesn't get used as much as it could due to the general lack of CC in PvE nowadays (I've used it as a clutch save on mobs going for a healer to give the tanks time to work) and a weak but better than nothing escape spell in PvP (if nothing else, it makes them blow that trinket or racial).
Since this has gone longer than I expected, barring any major announcements next week will conclude our talk about leveling with the new ranks of spells and abilities we've already experienced in leveling to 70 before Wrath.