As far as Roger being viewed as "underrated" here in the US, that just sounds like a way for Roger's fans and some well-regarded tennis observers to say that even though he's won "only" 6 Slams to date, it's acceptable to put him up as a candidate, right now, for greatest of all time. Many folks are doing that, and it's all so premature. For any baseball fans out there, it's like judging Koufax to be the greatest pitcher ever: he was great, but for a career, Sandy had only 6 dominant seasons, and that's probably not enough to say he was the greatest over a career. Same's true with judging Roger as the greatest while his work's only half-done.
Some of the ESPN commentating contingent fall into this group: in order to rationalize their excitement over Roger's brilliance and era-dominance, and to spoon-feed their opinions to us, they rush out and gloss over the fact that he's really only been at this peak since mid-2003, and that a measure of greatness is also to sustain it, not to just achieve it. For them, it's not enough to say he's great or is playing great; it's got to be jammed out to us that he's the greatest. Bull!
Not to take anything away, Roger is and has been Michael Jordan and all, but Sampras won 14 majors and was ranked number 1 for about 5-6 straight years in the 90s, so Roger's got a way to go. Frankly, I doubt he'll get it (averaging a realistic 2 Slam titles a year, he'd have to keep up this pace for 5 more seasons, and he's burning his candle right now 'cause he's over the top brilliant as we speak). Sampras also had many "money" wins; Roger's been stressed only a few times in the past 2.5 years, and his Davis Cup record (I look at that, anyway) doesn't have any Ljubicic-type moments.
I disagree that Roger's best is better than Pete's best, but who knows? Roger undoubtedly looks prettier doing it, but Pete was often devastating with his game and dominated for most of a decade. What separates Roger from Pete is Roger's inhuman ability to avoid bad or routine losses in smaller, workaday tournaments, and he wins just about every event he chooses to enter. How much longer can he keep that up? (Come to think of it, maybe I am underrating him ...)