Regs just get slightly better and more aggressive at each level. By 25nl i think many regs at least study to some extent and take poker semi seriously. Whilst 5nl and 10nl are similar. 10nl to 25nl is a bigger jump imo
Tighter ranges, more consistent game overall, more aggression and you'll see more 3-betting. Also agree with Station Master.....the jump from 10nl to 25nl is bigger.