It has more layer features and a tighter interface (as well as minot tweaks). The reasons I don't like it as mush are:

1) It's damn slow, even on a PIII 700
2) You can't turn layers off - it just loves making new ones
3) Tool pallettes "roll up", but their sizing is all ****ed up

It's not worth buying if you have version 5.

Just a thought