honestly, it makes the base game a little more random. you're hoping for potions to come up along with the correct amount of gold for you to make an efficient purchase. in an alchemy-heavy game, this can very easily be the defining difference in scores.
Seems like a solid expansion, after one play, I'd say it probably fits in easily as my 2nd favorite (after seaside). Games are a little longer (because the new tier of VP's means players aren't buying out the province stack as quickly).