The truenamer is basically ok, but requires the DM to be careful about allocating equipment.
If you use items only found in the Tome of Magic and the DMG, and start with a 16 int, you begin succeeding your truespeak checks versus an equal CR target on a roll of a 7 at level 1. You end at level 20 with basically exactly the same thing.
That's a better chance of success than most spellcasters will have casting spells versus their targets. So that's a positive. Your buff spells have failure rates, which is a negative. On the other hand, you have more uses per day than anyone else in the game, which is a positive.
One out of combat utterance can typically be used 8 times or so per day, because you don't care about the failure rate until it becomes completely impossible to use.
Because all utterances scale the way they do, a level 1 attack utterance like a reversed Inertia Surge is still viable at level 20 if its what you really want to do. And it just may be, a lot of utterances are generically useful.
Some people don't like the need for equipment to buff the truespeak check, but its built into the system. If you remove it, the "succeeds on a 7 at all times" mark is a good way to judge whether your "fix" is a good idea.
Level 1
16 int, 4 ranks, skill focus, = +10 versus DC 17. Succeed on 7.
Level 20
21 int, +5 int inherent bonus, +6 int enhancement bonus, 23 ranks, +10 truespeach amulet, +3 skill focus, +47 vs DC 55.
Luck Stone grants +1, Pale Green Ioun stone grants +1.
Succeed on 6.
I personally think its fine. Sure, a tricked out cleric can probably beat it, but... who cares. It contributes interestingly to a party and holds its own.