From what's been calculated, it looks like it's not actually that bad -- it's just relatively brittle. If you're facing 4 encounters with critters near or slightly below you each day,
and you have enough wealth to keep your skill checks up, it's balanced. If you have lots of encounters with low-CR critters, it's strong; when you face the "boss monster" with a CR above your level, it's weak.
Advice to player: It's all about the skill checks, holmes. Scour every book for feats, spells someone else could cast on you, Bardic music effects, and magic items which boost skills. Buy them or (arrange for your friends to learn them & use them). There's an Utterance which gives you a +5 to skill checks. Guess what should be one of your favorite Utterances? Yep.
Use Magic Device -- for when you can't affect a foe with your Utterances. Or for whatever. Get a bag of Wands and Scrolls.
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Advice for DM: Treat this guy more like a Fighter than like a Wizard. He's great against mooks -- so make sure there are some. He's also good for lots of fights each day -- he should be able to use each Utterance like 10 times (!!) each day before it burns out. Sure, he won't be able to do so
reliably near the end of the day, but the same goes for Fighters -- they can't always hit, but they can swing the sword all day trying.
Make sure this character has appropriate gear for his level.
Cheers, -- N