I know nothing about Neptune. That being said, I think that the Windows 2000 series was the one that they finally got right. XP was basically the same OS with some minor enhancements and a new UI that could thankfully be turned off. --That being said, MS attempted to 're-invent the wheel' so to speak with Vista, and even though Win7 was a slight improvement over Vista, it still followed the same paradigm, as has Win8 as well as any ensuing followup to that.
Instead of keeping things simple and straightforwards, they have made things more difficult and resource hungry than they need to be, just because they have the cash to do so, and because memory and processing power is relatively cheap these days.
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When There's No There to get to, I'm so There!