The first thing to say is that if you try and upgrade on the Big Day - July 29th - you may well find the experience frustrating. There is a reasonable chance that at least several million other people will be downloading it at the same time, so things could get a little slow. A better strategy might be to give it a week or two before trying. And before you try to upgrade, make sure that you've got a backup of your data. Just in case...
To recap, Microsoft have skipped a version after Windows 8 because they reckon the upgrade is so major that it is like things have moved on by two generations. We disagree - underneath the hood there has been quite a bit of re-engineering but from an end user perspective this feels more like a Windows 8.2. Which is to say that they have taken the ideas introduced with Windows 8 and basically polished them to a high degree, putting right the howlers. The headline feature is the return of the Start menu. Only it's not quite the same as in earlier versions of Windows as includes the app tiles that were previously on the Start Screen of Windows 8. If you want a 'proper' Start menu then you'll be better off downloading a program such as Classic Shell, which works as well on Windows 10 as it does on Windows 8.
In fact, looking at the Windows 10 Start menu gives you a good idea as to what is going on: the icons are chunky and this is to make them usable on devices with touchscreens. What Microsoft are trying to do is produce a single version of Windows that runs on computers, tablets, phones and the XBox. As such, it has to cope with keyboards, mice, touchscreens and so on and is able to adjust itself to cope with these sometimes differing requirements. It does so rather well: connect a keyboard and a screen to a tablet and it will start behaving more like a computer, as will a mobile phone to some degree.
This also explains the sometimes schizophrenic feel of Windows 10. There are often multiple and inconsistent ways of doing things, as though it has been put together by a committee who couldn't agree on everything. For instance, you can adjust some settings using the modern 'Settings' app, but for others you need to go back to the Control Panel. Or, you might be using Settings, choose an advanced option and it unceremoniously dumps you into Control Panel for the fine tuning. During the gestation of Windows 10, more and more features have migrated into Settings, but it is likely that the Control Panel will remain for some years to come.
Should you upgrade? If you like Windows 8 then probably yes, as it improves and refines things (and gets rid of unpopular features such as Charms). But if you prefer Windows 7 then possibly not as it is revolutionary rather than evolutionary.
If you do decide to take the plunge, make sure that Windows 10 drivers for your hardware are available from your computer manufacturers website. Case in point: we know of an educational institution that bought a large number of laptops a few years. The laptops were specifically chosen because they were totally silent - an unusual feature at the time - and because they qualified for a free upgrade to Windows 8. When Windows 8 was released they quickly upgraded them, only to find that the laptops' fans were now on constantly at full blast. It turns out that the manufacturer had a driver in Windows 7 to manage the fan but hadn't and wouldn't produce one for Windows 8. End result: a library full of silent laptops was transformed into one that sounded like living within earshot of a busy motorway.