Mesh themselves commented in an interview with Side-Line that folks who had heard pre-release recordings of the songs found them, "'it is definitely Mesh, but is Grittier and more Rockier than before."
My first thought is that I disagree. I think the sound is very similar to what Mesh gave us on We Collide. Back in the not so distant days when Mesh released Who Watches Over Me? or even The Point At Which It Falls Apart they were basically out-Depeche Moding Depeche Mode themselves. If anything, it was the period before that, In This Place Forever and Fragile that sounded grittier; a fusion of Depeche Mode from the late 80s and Pretty Hate Machine-era NIN. With We Collide Mesh introduced a "rockier" sound, although that's an ambiguous description. What do they mean by rockier?
Mesh did up the quota of guitars, but they're not usually hard-edged guitars. In fact, they're often acoustic. Perhaps it refers to the bass guitar sounding bass lines and analog drums. I don't know that they actually used a bass guitar (in fact I'm quite certain that it's sampled and played via synthesizer, but it sounds often like it could be a bass guitar. And this does give a sound that can probably best be described as "Rockier" relative to the overt synthpop. But if A Perfect Solution sounds like this, it's just a continuation of what they were already doing on We Collide. I also don't know that I'd say its grittier, except that We Collide actually had a couple of tracks that were upbeat and almost happy. A Perfect Solution doesn't. And I guess they use a few mild curse words more frequently, but I don't think a few "damns" and "hells" qualify them as gritty exactly.
In any case, those are not meant to be criticisms, just musing about the description, which I don't think I agree with. It's still a brilliant album. I'm reminded that I was going to do a series of posts about Depeche Mode imitators, and then I only ended up doing one, talking about Camouflage's Sensor. My next one up was going to be Mesh's Who Watches Over Me? But maybe I'll just do this one instead, after I've given it enough listens to be qualified to actually write a review of it.