If you are interested in serious mastering, then the new version(s) of Ozone are well worth a look. Versions? Well, yes - you can get the 'Basic' version for a very reasonable $199, but the Advanced version is going to set you back rather more, I'm afraid - it's $599, but get it before Dec 1st, and it's $100 cheaper, and if you already own Ozone 4, it's $399. One of the very tempting things about the Advanced version is that you can now utilise components out of the whole system as individual plugins. Also you get some rather posh metering options - important if you are trying to conform to more recent broadcasting level constraints (which I personally think suck a bit, but that's another matter, and hardly Ozone's fault!). There are also extra controls on many modules with Advanced.
Other Stuff:
One thing that is notably improved is the reverberation option - this has always been a bit of an Achilles' Heel for Ozone, and this is now completely revised, to some considerable advantage. One thing that I don't think is
quite so good is that in the exciter, the 'warm' setting isn't as effective as the Ozone4 one is (the developers are aware of what I think about this, FWIW)
Overall, this is a considerable upgrade - a lot of things just seem to run a bit smoother than they do in 4, and there are extensive opportunities to reconfigure it. One neat thing that's happened is that you get two opportunities to do EQ tweaks now - you can do it pre and post processing, and they've upgraded the EQ engines as well. Taken all together, the number of improvements is pretty impressive - as are the end results.
But, as ever, a warning; it's easy to overdo this stuff, and without a decent pair of monitors, a sensible monitoring environment and considerable restraint, you are just as likely to make things worse as you are to make them better.
You can find out more here:
Ozone 5 Complete Mastering System.