Based on a quick visit to Bratislava, my consensus is that Bratislava is deserving of a very quick visit.
At first I felt that it was in me to wax on the understated charms and bare knuckle beauty of this often overlooked post-soviet gem, but then I actually spent some time there. Considering it's approximation to other more deserving Eastern European heavyweights -- Vienna an hour to the west, Prague and Budapest equidistant on either side, and Krakow a few hours to the northeast -- who in their right mind would designate more than a 24 hour stopover to this highly unremarkable point of transit?
The #1 reason most travelers seem to visit Bratislava is that it's on the way to somewhere else they're going. That's why we went, and it's also why we effectively cut our brief visit into a briefer one -- after being dazzled by the highlight reel spoils of Prague, Bratislava's mildly amusing old town area and lackluster castle (with an offbeat blue church to boot) do not particularly impress. And with Vienna right next door, why would you con yourself into spending more time away from the legitimate contenders that surround Bratislava on all sides? In our case, we couldn't hightail it out of there to Budapest fast enough.
To be fair, Bratislava is surely a worthwhile place to visit. It has enough firepower to churn out a memorable weekend for those who are curious (or listless) enough to give it an opportunity. But about halfway through that weekend, you'll start to consider if maybe not every city in the world is worth the concrete it's sprawled over.
If you must have the Bratislava feather in your cap, plan on spending a maximum of 2 days there -- you can always back out halfway. Make sure to get lost in the old town area, stopping by the UFO Bridge and hilltop castle while in the vicinity. Sample some of the local delicacies, which are invariably composed of potatoes, wheat flour, cheese, cabbage, onion, and garlic. The Slovakian food is a high point of the Bratislava experience, but it is not entirely distinguishable from similar cuisines found in the regions surrounding it. The beer is also excellent here, but again, this is familiar territory for Eastern Europe.
I'm confident that there are many wonderful nooks and crannies to Slovakia that are waiting to be explored, and we do intend on returning for a more in depth investigation of what's on offer out there -- the Tatra mountains, the numerous lakes and caves spread throughout throughout the countryside, the excellent trekking opportunities...pretty much everything outside of Bratislava!