I have a good gaming PC, and a last gen console to compare my PS4 to, and I think it's performance is great for $400.
The PS4 doesn't outperform my main gaming rig, mainly due to CPU performance. Jaguar cores are very power efficient, and don't generate a lot of heat, but they're also very little cores, and they don't clock that high. A desktop CPU will generally be more powerful. This isn't usually going to be a problem, especially in single player games, but if you were in a multiplayer game with 50 people in an area, the CPU performance is going to be the limiting factor on FPS, IMHO.
GPU performance is great at this price point. You could argue that a 7850 with 2GB of GDDR5 could perform similarly in current games, and you'd be right... and they can be found for as little as 150 bucks if you find a good deal. But, on the other hand, a GPU in that performance range with access to 4GB of GDDR5, generally costs over $300. Consoles have less API overhead, and better optimization in general, meaning that a R9 270 would actually perform similarly, despite a slight MHz advantage, and a few more GPU cores. If you could find one, it'd cost about $200 (AMD's 180 price never will exist on the actual market), but most manufacturers don't sell those. They sell R9 270X cards instead, which cost roughly 250 bucks. And that'd still just put you about on par with PS4 graphics performance, with less available VRAM.
I personally think it's difficult to match PS4 graphics performance in a sub $700 gaming build. Trying to do it, factoring in a legit OS install (not pirated or Linux), Bluray, WiFi card, and 7870 or better GPU, with a i3 2120 or better (so the CPU won't be a big bottlneck), isn't realistic. Then try to do it in a good looking small form factor MiniITX case.
You can't.
On the other hand, most people need a PC for other tasks, and you can buy a 750Ti and drop it into pretty much any desktop and get superior to Xbox One graphics performance. It's a Dell system with a 300w power supply? Doesn't matter, with the Maxwell power efficiency improvements, this little guy doesn't even need an additional power hookup from a 6pin, just drop it into the card slot, install a driver, and bam! You're playing Titanfall with better settings than an Xbox user, more smoothly, and it only cost you 150 bucks.
But then, if you wanted to drag that system out of your office, and hook it into the HDTV in your living room.... you're going to have a bad time. The OS isn't designed for a controller, and you'll end up using some wireless keyboard with a trackpad or something. It'll be clumsy. The fonts will be small and hard to read, and none of your applications will be easy to use. You'll squint at your netflix, and you're GF will think you're a huge nerd.
While PC's have clear advantages, with flexibility in hardware, modding, and even cost effectiveness, it's consoles that are actually designed for the living room gaming experience. That's what they're for.
I can can browse a Youtube vid on my tablet, and send it to my PS4's browser, and listen through my controller. Netflix performance is better than any of my other non-pc devices. Everything in the UI is designed to be easily navigated with the wireless controller. The games update themselves (downloading updates in standby even), and the overall experience is just easy. Games run at settings similar to PC high settings at (usually) 1080p with FXAA. It just makes sense to use the PS4 in my living room.
Now, that's before even considering exclusives, which right now, aren't the best. I don't know if The Order is going to be good, or Infamous, and I don't even care. I look at a mountain of PS3 exclusives, with titles like Valkyria Chronicles, Demon's Souls, God of War III, and The Last of Us, and I feel really really re-assured that the PS4 will get important exclusives that I won't be able to play on my PC.
If you're a console only gamer, I pity you. No mods , or MOBAs, or RTS games, or city builders? Gross. But at the same time, if you can just ignore the mountain of great console exclusives, and just pretend they don't exist.... That's a darn sorry state of gamer existence to me too.