It isn't useless, and is not just a tablet OS.
The reason most people don't like it is because of the metro ui, rarely have I seen much different substantial criticism.
Aside from the metro ui, a different looking task manager, and a few other changes, it is fairly similar to windows 7. In my experience it feels a little snappier than 7, and there are a few other features that I like on 8 that weren't on 7.
Both OEM versions are the same price, although from what I've heard the way the licenses work are slightly different.
If you want a recommendation for me than go with 8, I have it on both my laptop and desktop and I like it. It took me about a week to get used to and now I am just about as good with it as with 7. Some of the issues that people have with 8 are apparently going to be lessened in 8.1. If you don't like metro ui then use desktop icons (that's mostly what i've done anyway). If you want your start menu back then look into Classic Shell.
Since you say you want a Windows 8 exclusive feature then you might as well get 8. If you already have 7 then staying with 7 might make sense as the 2 OS arent so different, but for buying new then 8 is my recommendation