I cringe in fear whenever I see rebuild on the board. As a relatively new (Goko) and somewhat infrequent player, my experience with the card is limited. When playing against players of similar rank, I already feel at a disadvantage due to my lack of experience in playing the mirror. As a consequence, in some of my games against it, I have decided to try alternate paths to victory.
Game 1Key Cards - Rebuild, Sage / Fool's Gold, Chapel, Cultist, Mandarin
My opponent makes a few mistakes (mainly buying Great Hall's instead of Sage) but the quick build up and consistency of Fool's Gold/Cultist makes quick work of Provinces while bloating my opponents deck. The Mandarin allows top-decking of 2 Fool's Gold for endgame play.
Game 2Key Cards - Rebuild, Moneylender, Thief / Chapel, Treasure Map, Storeroom
My opponent goes for Rebuild using Moneylender to both thin deck and purchase Rebuilds. The Thief is picked up in response to my going for Treasure Maps. By golly this was a tense game. I could hardly believe how fast Rebuild chunked through the VP piles. My opponent managed to gain a single Gold from me in his one Thief play post Treasure Map trashing. Storeroom really is the key card here. A play of Storeroom means I only need 2 Gold from 6 cards to guarantee Province. Without this card I don't think it could have beat Rebuild.
Game 3Key Cards - Rebuild, Cellar / Tactician, Noble Brigand, Rebuild
I go into this game planning on Rebuild. Unfortunate draws of $4/$4/$4/$4 on turns 3, 4, 5, and 6 combined with every Noble Brigand buy/play missing Silver make the mirror impossible and I flounder around with Tactician.
Game 4Key Cards - Rebuild, Sage, Warehouse / Forager, Highway, Moneylender
This is a really good Rebuild board but I go for the Forgarer/Highway combo. In hindsight, this wasn't the best choice. There is no net gain +draw available and the only +Buy is Forager which needs fodder. Once greening starts, it's going to crash and burn. Perhaps I could have tried something cute like get 4 Highways and try to buy out the Duchies, then transition into Rebuild for the last Provinces, I dunno. This was an interesting game regardless of the outcome.
Game 5Key Cards - Rebuild / Throne Room, Market, Steward, Goons
So Rebuild clearly isn't the best choice here but it highlights a key aspect of playing against Rebuild. When the non-Rebuild player doesn't need to compete for Provinces, they have a huge advantage as they can have more available turns in which to build their engine and gain points.
So my take-away thoughts from these game are that Rebuild is really really good. Even without much support, it can define a match and give an exceptionally fast baseline that other strategies must compete against. Give it some good support and it is even more intimidating. But it is not unbeatable. Perhaps that's what makes dominion such a great game. A great card like Rebuild though good, is not game-breaking.