The CSS support is better. A number of crippling bugs that plagued web devs are banished. However, the thing is very much bolted on and there is a lot of CSS 2 that is improperly or not implemented. It is still way behind Gecko (Mozilla), Presto/Merlin (Opera) and KHTML/webcore (konq / Safari). Lots of great techniques will still have to be hacked round, and web dev time wasted...
DOM (i.e. standard javascript) support is rubbish.
Regarding the UI / features, blatant imitation is par for the course, Microsoft are pretty good at it. However, claiming Firefox as precedent is quite funny — it was originally designed to imitate IE