Spell Blast is an interesting counter-spell, in that you have to pay X where X is the total converted mana cost of the spell you're trying to counter. Obviously, there are far better counter-spells than this, but in a Limited setting, it's decent to have early game, but has greatly diminishing returns as the game wears on.
This was a card that was a bit better in the early days of Magic, though good old Counterspell for two blue mana greatly outclasses this card. Spell Blast is mostly worth mentioning because it's in the Magic 2014 Core Set as an uncommon when before it had only ever been printed at common, where it belongs. It's an OK Commander card in a counter-heavy deck, but who wants to play against one of those?
It's certainly an okay common card, but why Wizards decided to reprint it at uncommon so many years later befuddles me. That's Wizards for you, reprinting the seemingly most random things for the sake of Limited play.