The blinds come around quicker, meaning we should open our ranges up a touch (generally though, in the early levels in the micro limits, playing tight is really optimal)
You have much more play in a 6max game in my opinion, you have more time to get reads and outplay people in postflop situtations.
The late game is relatively the same, the main differance being the bubble factor in 6max games is much higher than the 9 man games. (Doing a study of how the bubble factor differs in both formats tonight, i'll post it later ITT)
You have a ton of interesting/tricky bubble decisions, the stacks can change quickly and you need to have a pretty solid bubble game.
But, opening up isn't just a matter of playing more hands, you actaully need to be good playing postflop, otherwise you are just setting yourself up to lose.
Overall, i've played around 6000 9 mans, and only 500 6max games, but for the most part i've found the 6max games far more enjoyable. They seem to be a lot looser, and the regs and fish are really bad for the most part, so playing a tight/agrro style can net decent results i believe.