I think III is, musically, the best album they've done. The sales were bound to be down compared with Progress because - no Robbie, no Jason, less fanfare on release, These Days not being as good a lead single (thought it's still a great song IMO) etc. and just general attitudes towards the band changing.
Though there isn't a bad song on the album. Particular gems are Let In The Sun, Freeze, Flaws, Give You My Love, I Like It, Higher Than Higher.