The main problem with counterspelling is that you need to have the appropriate spell available. While just about every arcane caster can cast Magic Missile 24/7, a Flesh to Stone, See Invisibility, or Rainbow Pattern can really ruin your day. If the enemy spellcaster notices you readied for counterspelling, he's not going to cast Fireball, since youprobably have it. He'll cast Sleet Storm to blind you and then follow up with Fireball when you can no longer counterspell him. Unless you keep two or three Dispel Magics prepared and never use them for actual dispelling, it's hard to keep up (although, admittedly, this is one area in which the sorcerer can shine. I've never seen a sorc without Dispel Magic).
To make counterspelling viable, the counterspeller should be able to counter with a larger number of spells. Perhaps any spell of the same level. Or, just handle it the way Arcana Evolved does: one feat gives counterspelling as a caster power check with no loss of spell slots.