The new Mac Mini (2014) is praised as a significant upgrade in most of the early reviews. And there are some improvements, most notably two Thunderbold 2 ports, (slightly) improved graphics performance in the two lower-priced models (Intel 5000 integrated graphics rather than 4000), and (even more) improved in the higher end model (Intel Iris Graphics). However, there are two changes that I can only consider as evil: You could easily upgrade the RAM yourself in the models from October 2012 or earlier. Apple has eliminated that possibility. In other words, you now MUST buy the ridiculously over-priced memory models and pretty much have them installed at the apple store (though I am sure that clever users will find ways to circumvent this). Nor is there a four-core processor option available any longer.
The last two "improvements" will keep me from buying the new model. I will stay with the four-core 16 GB 2012 model I now have until the next "upgrade" or until I buy another non-Apple computer. The last decision will depend, of course, on the next version of Windows. I can't stand Windows 8.
Update on October 19th: See also here. The Ram is soldered into the motherboard. The screws at the bottom of the device have been so modified that they are "tamper proof." Opening up a Mac Mini to change the hard drive means a voided warranty. That means no Mac Mini for me any longer, and probably the end of my Mac experience (after the Mac Mini 2012 will be obsolete—which may, of course be a while). I do like the the operating system, but not so much as to give up any possibility of modification. Case closed—no pun intended :).
Later that day: It keeps getting better: "Unlike single-core performance multi-core performance has decreased significantly. The "Good" model (which has a dual-core processor in both lineups) is down 7%. The other models (which have a dual-core processor in the "Late 2014" lineup but a quad-core processor in the "Late 2012" lineup) is down from 70% to 80% See here for more.