http://boardgamegeek.com/boardgame/98778/hanabiI got this game for Christmas and have played it with a variety of groups of people. Nobody in our groups has yet to see a game with a perfect score of 25 (so we haven't broken out the rainbow cards yet) but I have a few observations I'd like to share.
Hanabi seems to be best played with the same group of people -- I find myself having the most fun when I've played a few games with a particular group and we can really open up our play style. With different players who think differently, the group doesn't really function well and it can be frustrating. With a group I'm familiar with, we keep finding new ways to insert subtext into our clues and it's a lot of fun when it works (and when it doesn't work)
Newer players seem to want to give lots of clues -- and this is a really bad thing. One of the worst things you can do is to have a play (play or discard a card) given to you and then not do it, especially if you're going to spend a clue token. Is it due to a fear of discarding an unknown card? Playing an unknown card? Usually in games with people like this I find myself just blind-discarding cards the whole time because running out of clue tokens is really bad.
Our group has found that blind-discarding, especially in the early game, is quite a good thing. Don't know what to do? Blind-discard your oldest card! It's predictable (so people will know to warn you of important cards you're about to discard) and it gets information out there when we can't find any good plays to make. It's much better than giving clues about discardable cards (which, the more we play, the more we've realized that this is pretty much never a good idea).
Standard protocol seems to be that if a clue is given that singles out a card in someone's hand, that card should be played (unless it's clearly impossible, like I'm telling you about a 5 in your hand or something weird.)
I really enjoy some of the more "meta" clues we give: A says "B, I'm going to give you a clue; C, this card is a 4". Now it's B's turn and he knows a certain card in his hand is yellow, see C's yellow 4 in hand and knows his yellow card must be a 3 that plays -- two clues in one by slightly abusing the phrasing of a clue (which is still technically within the rules of the game).
Does anyone else have any fun "meta" clues or protocols their group uses to squeeze in more information? Is a score of 25 really possible without something that's blatantly cheating?