Seems like the site's differentiating feature was multiparty escrow transactions but weren't used often due to hassle?
Not with Bitcoin. With multi-sig transactions you don't have to trust the escrow agent to not steal your money (assuming you're confident the escrow agent is not also the other party in the transaction): https://en.bitcoin.it/wiki/Contracts#Example_2:_Escrow_and_d...
As dshankar pointed out, Evolution supported these types of transactions but they were not widely used, presumably because they are more difficult than normal transactions.
Probably because no bitcoin clients that aren't 3rd party (blockchain.info wallets) offer multi sig in an easy to use UI so nobody could figure it out and just trusted the admins of Evo.