If a transaction shows up in a block that uses an arbitrarily complex, non-standard script (but doesn't use any disabled op-codes), it will be accepted by all the nodes as long as it is a valid script (and if it's a TxIn script, that it evaluates to true with the TxOut script being spent).
However, the act of getting such a script into the blockchain is fairly difficult, because no Satoshi-based nodes will relay transactions with such scripts, and no miners will include those transactions into the blocks they are producing.
What this means is that, you can use all the advanced scripting capability that isn't specifically disabled, under two conditions:
(1) The scripts are ultimately valid
(2) You mine them into a block, yourself
In other words: no one will help you put those scripts into the blockchain, you have to do it yourself by solving your own block. But those blocks will be accepted as part of the longest chain once it's there.