I really like the Unison sound, it's very close to the style I spent years trying to perfect in SynthEdit.
A low-pass filter should sound dull, as it's removing the high frequencies. The filters certainly aren't hugely characterful but they do the job and with built-in Drive and very comprehensive routing options, they offer a massive amount of flexibility/versatility.The filters sound "dull" if thats the right word to describe it.