Decided to play a match against the bots real quick. Didn't finish but it had some alchemy cards in it. I must say I actually enjoy the mechanics of Alchemy. I heard that it wasn't well received. Why is that?
And on that note...how do you know how many potions to buy? Lol. I was trying to balance that with treasure and kingdom cards and it was hard!
Whatever you do, don't pay attention to how many Potions the AI buys. Sometimes it will buy 5 or 6 of them for seemingly no reason. You probably want at MOST three, and that's only for Vineyards pretty much. In 90% of cases where you want Potions, one Potion is fine. Oftentimes you can ignore Potion cards too. It all depends on what's in the kingdom.
As for why people dislike Alchemy, I think a lot of it's because IRL several of the cards are obnoxious to play (Golem, Philosopher's Stone, Possession...) for various reasons, and adding Potion costs to things complicates how some cards work unnecessarily. Personally, Alchemy is one of my favorite expansions, though. It and Guilds are the most 'out there.'