The latest mini manages to feel a little snappier in operation than the last generation system did. I'm not convinced improved specs can be held wholly responsible for that improvement though. It seems much more likely that the performance enhancements in Snow Leopard - such as the 64-bit rewrite of its core codebase and the enhanced multithreading management offered by Grand Central Dispatch - are largely responsible for that. Whatever the cause, though, the result is what matters and even running multiple applications, with mutiple windows for each, the Mac mini never felt unresponsive.
Criticisms, then, are no different now than the last time I used a Mac mini. The use of mini display connectors mean there's space for two at the rear, but having to use an adaptor to get an HDMI output isn't ideal considering the mini would otherwise be a brilliant under-TV PC. Imagine the lost adapter revenue Apple would suffer were it to use standard connectors, though! The company is only barely in the black after all.
More problematic to the Mac mini is the newly updated iMac range. The cheapest of these is 'only' £450 more than the cheapest Mac mini and has better specs. Comparing with as close to identical components as possible (£649 for the Mac mini, £120.01 and £79.99 for the 2.66GHz CPU and 500GB hard drive upgrades respectively) the difference shrinks to a mere £100, which is bloody good value for a 1,920 x 1,080 pixel, LED-backlit display. Oh, there's a £55 Magic Mouse and a £28 keyboard bundled with the iMac, too, making the difference ludicrously negligible.
Now I'll be the first to admit there are few Mac mini users who need more than a 2.26GHz Core 2 Duo processor, 2GB of RAM, or a 160GB hard drive (we should all be using NAS appliances anyway). Nonetheless, I wish you good luck finding an LED-backlit 1080p monitor, plus a keyboard and mouse, to pair with the £499 Mac mini for under £450 and even if you can, the result won't look as elegant - that I'll guarantee.
Okay, you may not want or need the 21.5in iMac's size and resolution and don't care about the numerous benefits of LED-backlighting. And yes, it's entirely possible you already have a serviceable display on your desk. But neither of those considerations change the fact that in many, if not most, situations the iMac, all costs considered, is a better value solution. Just rest assured that if you are one of those for whom the Mac mini is a better option then it is a fantastic system.
In isolation the Mac mini is a fantastic entry level OS X system. Unfortunately for Apple, the latest entry level iMac is so well specced and so well priced that there are few situations where it wouldn't be a better option.