Grima is amazing.
I would go so far as to say he is one of the strongest solo heroes in the game. Still good in multiplayer but you will get some groans about threat raising everyone's dials each round.
But what a strong trade off, for the low cost of one thematic threat raising his poisoned counsels will reduce the cost on ANY sphere of card that you play next. Blanket unconditional cost-reduction is an incredible things. Some examples, being able to play Resourceful, Sword-thain or Treebeard Round 1, in a tri-sphere deck with leadership being able to play Steward of Gondor round 1. In Saga campaigns you can drop a Gandalf Ally any round, even if you start with no resources. Also when compared to other resource-generating characters or effects, Grima can't lose that resource from a treachery card, can still use it even if you can't spend resources, and it's always in play at any point of the round. Grima accelerates your game and combines extremely well with Lore's massive card-drawing effects.
For further craziness combine with Mutiple Masters of Lore and Damrod and you'll be playing the majority of your deck in no time at all. If you haven't tried Grima yet, give him a go. Also combined really well with keys of Orthanc to earn you money of the money you arne't spending. The king's counselor is an excellent addition to any trio of heroes.
Pairs really well with Erestor, Damrod, Galdor, Berevor, Bilbo, Pippin or Ori as their card draw will help give you options for Grima's resource assistance. Lore Aragorn also works well with the Rohan counselor to bring your threat back down later. Cost reduction characters like Theoden and Damrod can stack with Grima for free allies and traps each round.
Sample decks: ringsdb.com