There is just one problem - counterspelling itself is generally quite sub-par and deemed a serious waste of a good standard action. You are wasting an action not doing anything, and you getting to act hinges on the PC spellcaster doing something. If he catches on, he can simply opt to do nothing, while the rest of his party closes in.
IMO, it really only becomes worth it at lv27, when your caster can access the epic counterspell feat (which lets you counterspell an unlimited number of times each round as free actions).
Also note that spell power was revised to now give +1 caster lv instead of improving your spell DCs.
The PCs have the advantage with their 4-5 actions to the wizard's one each round, so you need to even the odds (typically by attempting to spam as many spells as you can). Make sure you are able to manage 1 quickened spell each round, and you can never have enough timestops to cast those crucial spells (this is where archmage's SLA power comes in handy).
Consider judicious use of sculpted spells (fairly undercosted for its benefit,
IMO) so you can consistently catch at least 4 PCs in the AoE of whatever you are throwing at them.
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