Last night I played a few IRL 3-player games with cards randomized from
this set of 25. The first game we played was with the following kingdom. I think this illustrates what is difficult, yet interesting, about 3 player games.
Courtyard, Lighthouse, Village, Wishing Well, Gardens, Mining Village, Throne Room, Trader, Festival, Witch
In two player kingdoms where both Provinces and Gardens are viable, you would decide to go for a Gardens strategy or Province strategy. It will be a mirror (Gardens or Provinces) or not. If not, the Province player will have to decide how many Gardens to get, as well, or just rush to end the game before Gardens is worth enough -- or the Gardens player rushes to end the game before the Province player gets going, maybe spiking a Province at some point.
However, in three player, if one player decides to do something different from the other two, he has
an additional advantage from a relative lack of competition for cards. If two players go for Provinces building an engine, the third player can get all 12 Gardens himself; maybe even before the other two players split the 12 Provinces -- Gardens only needs to be worth 3 for the Gardens player to be competitive here! It's not as good for a Province player to block by buying a few Gardens here as it is in two player. The OTHER Province player will probably win the Province split and the Gardens/Duchies won't be able to make up the difference. So, either the Gardens player wins, or the other Province player wins. Similarly if two players try to split the Gardens, the lone Province player can keep racking up the points.
In the game we played last night with the above kingdom, I decided to first grab a few Provinces then transition into Gardens. We all started off by grabbing engine components. I got two Traders and tried to pick up as many Festivals as I could. I grabbed two Witches and a Courtyard to help with draw, but I avoided thinning or grabbing Lighthouses. I should have just gone with one Witch at most, though -- my friends were pretty loaded up on Lighthouses and Traders, especially after I bought the first Witch. They both went for a thinner deck and were pretty clearly going for Provinces. After grabbing a couple Provinces and emptying Festivals (well, we all fought over those), I transitioned to Gardens. I passed on an opportunity to Trader a Province, which, in hind sight, I think would have been very reasonable to do. Once I made my transition to Gardens, I was able to rack up the cards and the points (extra buy Coppers became Silvers at a few opportune times, too!), and my friends were stuck with thin decks competing for Provinces. Both knew they needed to block my Gardens, but neither did. I got 11 of them and won by 15 points.
I think if everyone had planned to transition from Provinces to Gardens at some point, the game would have been really close even though we had different ideas about which components on the board were most important. Two players committing to Provinces all the way led to a Prisoner's Dilemma for them -- and a win for me!