The bass isn't wonderful, but that's hardly surprising in a unit this small and it's by no means the worst I've ever heard either. If you want to give it more punch, there's a bass boost button on the top of the device next to the Bluetooth button and volume control. This fills out the sound and gives it a bit more body, giving the impression of more bass, even if it doesn't add proper, low-down grunt.
There is one catch, though, and it's one that might get on your nerves if you notice it. If you turn the volume up, a small amount of high-level distortion at the top end of the audio spectrum is audible. It sounds a bit like someone rustling sweet wrappers in the background. But it's not something you'd hear if you were simply using the device in a party situation or for background music.
Incidentally, the speakers seem fine when playing the same music over the line-in connection, so it would appear that it's a problem with the Bluetooth decoding electronics rather than the amplifier or speakers within the unit.
Parrot's Party speakers are certainly well-designed for listening to music on the move. You can use them to play music from your phone, MP3 player or laptop without wires; they're compact and solid enough to travel with; and Bluetooth pairing works about as well as you'd hope it would. At £80 they're also pretty good value considering all the extra technology and, despite the distortion at the high end (over Bluetooth), general sound quality, volume and battery life is good for a device this small.