I got Blast Factor and honestly I don't think it was worth the $7.99 or whatever I paid. It looks really nice and it's fun to play every once and a while. Also when they open up 2 player support it'll be more fun - but as of now my play of it has come to a standstill. There really isn't anything to work for or unlock and the levels don't differ too much at all from each other.
I'd recommend the $3 Lemmings way before I'd say you should buy Blast Factor. Lemmings has always been fun, and with online user boards to compete with on every single level (50 total), you really can't go wrong.