Haven't seen Modern Family or Two and a Half Men, so can't judge. That destroys my ability to judge.
However, I will say that I stopped watching The Office a bit after they resolved the main romantic conflict. It was still kinda' funny, but it lost a lot of its charm when that conflict no longer existed. Now that Steve Carrell has left, perhaps its time for it to call it quits, but I can't really judge since I haven't seen the last couple seasons.
The Big Bang Theory isn't the greatest show ever, but the nerd-related humor is hilarious. It's embarrassingly and sometimes insultingly overexaggerated, but such is the nature of comedy. Its references to actual, real icons and culture really make it.
How I Met Your Mother is the standout of all these, as it's an absolutely brilliant show. The writers constantly astound me with their extremely rare ability to combine real, emotional drama with hilarious comedy. The story and characters are no less compelling and worthwhile than the comedy, and that's a truly great accomplishment. This is one of my all-time favorite shows, and it should never be canceled; it should end when it's made to. It's been going for a long time, but it's all working toward a specific ending, all building up to it, and thankfully it has at least two more seasons to do it in.