I've been running a basic self-enclosed HTPC for a few years now, and once set up it's pretty low maintenance. The most important thing I've learnt is that if it's working, don't try to improve it as I've always ended up causing more problems than I solve!
Mine is a simple MicroATX running an IvyBridge i3, set up in an Antec Fusion case, with 2x2TB "green" drives and an 80GB SSD for the OS, a BlackGold TV tuner to provide 4xFreeviewHD tuners, and a Hauppage for SCART input from the Virgin cable box (the BlackGold is technically capable of doing this too, but it never worked reliably for me), running Windows 7 Media Centre. I've found Media Centre to be very family-friendly and wife & kids are happy navigating round it using a standard MCE remote (replaced with a Logitech Harmony 700 a couple of years ago). I've never tried any other software as the kids use Xbox360/One's in their rooms as Media Centre Extenders, so I can't speak for how well other systems work.
The only thing I did have issues with was NetFlix, which I couldn't fire up from within Media Centre. In the end I spent £10 on an "eSynic KB05" mini keyboard & touchpad and it's been brilliant. It makes searching NetFlix so much easier than a remote and so we just have that and the Harmony in the front room and simply switch depending on if we're watching TV/Blu-ray/films or NetFlix/internet.
It's certainly nowhere near as easy to set up or maintain as a Sky+ or Virgin/TiVo box, but this is like saying a laptop is more complex than a DVD player - yes it is, but in the right hands it can do SO much more. I love having an HTPC as it means I have one central system for whatever I want to watch/do, rather than switching between the Sky Box, Smart TV menu and Blu-ray player/music amp.