There are many audio mastering situations where Ozone 5 is an excellent tool - even for pros - and even in many music production environments. It hardly depends from your expectations and applications. I use it in over 90% of situations at the very end of the master chain, but without any shipped presets (they may be helpful for greenhorns during learning phases).
Ok, ozone 5 "sounds" very neutral (as "requested" in many modern music scenarios). If you await very tonal, non-linear, non-digital or vintage equipment character of the components Ozone 5 alone could come at his ends if you don't like the usuable analog and/or saturation / exciting algos of Ozone 5's components - this is the reason why i often use it together with single or a few other plugins i.e. from WAVES and one reason why iZotope offers the modularized advance version for even more flexibility in such apps.
The dithering algo of Ozone is one of the best available on software market and the thoroughgoing mid/side multiband processing is very helpful to me. The measuring features round this - even without the metering suite of the advanced version.
Not at least: The VoS plugins seem's just VSTs on windows - for me, as a Pro Tools 11 on Mac user VSTs are just the very (!) last choice.
I could recommend Ozone 5 - i.e. together with a WAVES bundle like Silver or Gold - both versions available hardly discounted from WAVE from time time (around 65-80% plus 10% with this promo code from WAVE online: http://refer.waves.com/Ixex ).
For home to semi pro home rec users this might be (at the time!) a really cost effective alternative to get a professional basic toolchain not only for mastering.
Together with i.e. additional (discounted) WAVE saturators (i.e. Kramer Tape / Aphex vintage aural exciter or similiars) or even hardware effects many typical musical tasks could be done on a relatively high level.
btw: I tried to buy a Ozone 5 license used / second hand on ebay over monthes - without any success (did not find ONE used license in that time!), but it helps to deal out better prices on the list of Ozone 5 offers from the usual european and US music software shops there.
At last: Anything could be done "better" in special situations with more ressources (equipment, money or "just" time). To get out professional results from Ozone you need to know what you are doing too. Just pressing in some default presets may help in the learning process but will not lead to pro results in most cases.
I like the intuitive and clever user interface of iZotopes Ozone 5 and Alloy 2 and have some other iZotope (instruments/effects) plugins too - but this may depend from each ones taste. If you get it it is worth to read the user manual in detail as they hold many useful hints - i.e. to get even faster to results you want.
this is what i expect on such bunch of deep mastering (only) algos in a native software based mastering process (at least if i trigger/use some of the resource affine Ozone 5 features) - this one reason why iZotope offers Alloy 2 (which is the "lightweight pendant" of oZone in many parts) for mixing / as channel strip. But i run it on an old 2010 Mac 6.1 2.6GHz / 4G RAM (upgraded to (GB now mainly for sample space) without any bottlenecks beside other resource affine mastering modules in the same session (and sometimes even the master of a complex mix - without any DSP or acceleration stuff). So may be your PC is somewhat suboptimal configured or the Win/VST Version of Ozone 5 works suboptimal.