Well, if you want a bit of isolation and no sound leakage, the Koss 'phones -- as widely praised as they are, for the price -- aren't going to do it.
I just got my Creatives, and my first impression is that, in their class, they're fine. I've ridden tricycles with rusty pedals, and the Creatives don't sound that bad ...
They're not as refined as my Etymotics or my Shures, but I think they'll be better than my "fun" sounding Sony's (which also get criticized a lot around here, but also are good for what they are). For their price, the Creatives are fine. If you're likely to upgrade soon, jump right to Etymotics ER-6i's or Westone UM1's, instead. But you will need/want canal phones of some type/category if you don't want sound leakage.
I agree completely..the creatives/sennheisers have been overhyped in my opinion, but they definitely are good for what they are, cheap iems. If you're looking for higher quality, refined sound, definitely jump to the etymotics/westones/shures/ue. I know I should have, now I am...westone um1s should be here in a couple days.