Win8 has been real nice on my HTPC. I think if you're happy with 7, 8 isn't a major change (unlike going from XP to 7) but I think the default interface looks way nicer (Aero is fugly, I always reverted it to 'classic'), the DPI scaling seems improved as everything looks better on my TV and I appreciate the effort I didn't have to put into making it look nice, it just does. I was pleased that the codecs I rely on all worked straight away and I didn't bother installing a single driver except for the GPU and everything has still worked flawlessly right off the bat, including my wireless mouse and KB.
The new UI is basically a glorified start menu/desktop hybrid. You can use it as either really, I use it (a little) as the former. I don't understand why people are so up in arms about it. It took me all of a few minutes after I installed Win8 to get accustomed to where things are; the only time I see the Start screen is when I would access the start menu, which is almost never.
Default programs I'd agree aren't the best, but I think the problem with them is not their functionality but their interface. If an "app" is going to be run on multiple platforms, it needs to expect multitasking and non-touch input. Something as simple as a built-in minimize/close would alleviate much of this; or maybe MS could build an overlay for them. But even then, I haven't installed an "app" or wanted to yet, I just put all my normal programs on there no problem. If you want Firefox to not switch to desktop, then you'll need a Firefox "app". All the same, I think multitasking in the new UI could be more intuitive.
In general, there's "legwork" and some level of incompatibility between any version of Windows. I think they're valid complaints, but also hardly specific to Win8. While I think Win7 is great every time I use it for the first time I know there's still a lot of very specific steps I have to take to make it work and look how I want it to.