Is a 25 pound pack "bad" and a 15 pound pack "good"? Not necessarily - but, personally, I'd prefer to carry the 15 pound pack because I'm older, and not in the greatest shape. However, that wasn't what took me under 20 pounds for a weekend. Rather, it was pursuit of simplicity, the desire for an uncluttered corner in my life, that did it. As I relentlessly simplified my style (replacing 2 pots, a bowl, and a cup with a single kettle that filled all those functions, for one example), the pack got lighter and I got happier on the trail.
Depending on your style, 25 pounds may be perfect (to keep things apples-to-apples, we'll assume there's no difference between what you're doing and what I'm doing, thus no "mission hardware" - as Jimshaw calls it - needed.)
As far as carrying ability, they say 20 to 25% of your body weight is a reasonable comfort target (you can carry more, it just stops being comfortable.) I'd amend that to say 20% of your ideal weight, with any excess counted as part of your load. For example, if your ideal weight is 180, but you weigh 200, your reasonable load would be 36 pounds at 20%, 45 pounds at 25%. Deducting the 20 extra pounds you're carrying around gives you a target pack weight of 16 to 25 pounds - not the 40 to 50 pounds the gross weight calculation gives.