I know a lovely little hostel you can stay in...

I've done the day-trip from Vienna a couple of times (by train rather than boat - never could get organised in time to do the boat). By train, you have the option of a swish, new, fast train to the incredibly inconvenient Bratislava-Petrzalka or an ancient one-car railcar through some bizarre border backwaters to the much more convenient Bratislava hl. st (a short tram ride to the old town). I prefer the latter, but then I like things like that (I'm actually disappointed that it now runs through, and that you don't have to hop off on to the tracks at the border, wait for the police to turn up, and then hop across the tracks to an even more ancient one-car railcar).

The old town has been very well restored, with some lovely squares and back streets that are good for wandering around. You can get decent food and drink for very cheap (some of the more back-street bars do have some raw meat dishes that I wasn't too keen on, though...) At weekends, it can be popular with heavy drinking groups of lads who come from all over (not least from the UK) to take advantage of the cheap prices and behave accordingly.

It's a good place to wander round, explore the old back streets, and look at the bizarre welcome-to-our-alien-overlords boat over the Danube.

It does have its seedier side, and it does have its organised crime. The two often collide in nightclubs and strip clubs. You probably won't come across this, but it's a good idea to make sure you don't.