I am currently making a transition from NL25 to NL50 and so far I have few conclusions..
I feel that NL50 players tend to be somewhat more scared in putting their money in the pot PF so there is somewhat more limping.. They also tend to float you more when you raise PF and CB when heads up... I have also noticed quite a few players that are willing to put their stacks in on turn on a complete and utterly nonsense bluffs...

Anyway, I feel that the main difference is that players are tighter then at NL25 and they float more... this alone makes it a bit more difficult environment to play in, especially when your AK or AQ misses the flop.. I have to get more hands in to confirm what I just wrote but initially, it seems so...