I'm playing a storm-themed Evoker right now, and I looked long and hard at the Stormcaster. Unfortunately, our campaign will end around 8th or 9th level, so to me, this PrC just isn't worth my while. Later access to 4th and LOST access to 5th level spells isn't justified, and I won't get Thunderbolt.
Stormcaster? Kinda... meh, if you ask me.
Thunderclap? That's OK, in that you can always do a little bit of blasting and BC even when memorizing mostly utility spells, but it doesn't actually make you better at blasting. Spontaneously exchanging a spell slot for something else is always nice, though.
You gain +2 caster level on a bunch of spells, which is great, but you also lose out on a level of spellcasting advancement at first level... it just doesn't add up to something above-average.
The abilities which make you resistant to wind effects, ranged attacks etc. are OK, but again, nothing special there. Most of them (electricity resistance, Shield of Winds) can be emulated or trumped with low-level spells.
The only really worthwhile ability comes at level 5: add a bit of sonic damage to blasts, and a 1 round save-or-suck, which is the main selling feature. It has to do a lot of heavy lifting, though, since it's really the only thing that stands out. It's good. But compared to just going Incantatrix and adding a bunch of free metamagic to your storm-themed spells? I don't know.
Stuff I did with my character: first of all, the DM was OK with me taking a reskinned Bloodline of Storms: +2 CL to electricity spells (instead of fire spells) goes a long way. Energy Sub (electricity) was a given, and I've taken Born of the Three Thunders. Sure, using the feat dazes you for a round, but unlike ALL other metamagic I know of, it can be applied on the fly. It also doesn't increase spell level, and the effect is pretty sweet on a damage-over-time spell (HOLY SHIT energy sub'bed Kelgore's Grave Mist triple threat deathtrap!!!), or a spell that allows multiple attacks. A touch spell can also be good with this (cast this before entering combat, take your round of dazing, and hold the charge until needed). And I'm very much looking forward to energy sub'bed BotTT Flame Arrow for the party's archer...