Design and Build Quality
The 2010 Mac mini had a slot-loading SuperDrive, while the 2010 mini Server did not. This year, it's impossible to buy a new mini with an optical drive. Apple has a long history of killing off ports and accessories before the PC world. The floppy drive vanished way back when, and eventually the DVI port started to fade from Mac notebooks. And now, it seems the optical drive is next on Apple's hit list. Of course, the machine is $100 less than last year, so it's not like the loss in functionality comes without a discount, but what if you want an optical drive?
As with the MacBook Air line, this is a decision you'll have to make for yourself. Were you planning to use the mini as an HTPC, and make a few Redbox runs every so often? If so, this machine clearly doesn't have the hardware for you. If you were just looking for a compact, small machine that you could easily install vertically and not have anything to worry about in terms of heat / noise, then the mini might be intriguing.
It's typical for an Apple machine to maintain a clean look throughout. That's definitely the case here. The mini is one of the cleanest, sleekest desktops we've seen. The shell is all brushed aluminum save for the black rear (where the ports are) and the black circle/lid underneath, which can be easily unscrewed to remove user-accessible RAM (two slots). Ports on the rear include: an AC power port, 10/100/1000 Ethernet port, FireWire 800, HDMI socket, Thunderbolt (also supports DisplayPort), four USB 2.0 ports, an SDXC slot, audio input, and a headphone jack.
Internally, there's more power than has even been crammed into a mini before. The 2.3GHz Core i5 is a significant upgrade over the Core 2 Duo that came in last year's model, and the memory hums along at 1333MHz instead of 1066MHz. The 500GB HDD is pretty sluggish at 5400rpm, and strangely, Apple only offers an SSD on the more expensive $799 model. You can't even upgrade to it on the $599 build. Sadly, while the RAM is easily accessible, you can't access the HDD easily. So swapping in an SSD after the fact will prove to be a challenge for some.
In use, the machine never gets hot and noisy, even under stress. It's pretty impressive, actually. And these facts make it ideal for HTPC use; again, thwarted somewhat by the lack of an optical drive. Apple has also figured out how to shove the power supply inside the case, so there's no power brick at all. It's a positive step; these small machines tend to have power bricks that are nearly as big as the system itself.
All in all, it's a super sleek system, but there are obvious limitations to the size. No real expansion options, no optical drive, etc. That said, having Bluetooth 4.0 and 802.11n Wi-Fi within a desktop is handy, and Apple throws in an HDMI-to-DVI adapter for those still using the (slightly) older connector.