Every NCAA tournament game is difficult. As well as conference games.
One quick thing of note though is that most teams that make the final four really aren't that much of a surprise.
2000 Michigan State, Wisconsin, Florida, North Carolina
2001 Duke Arizona, Michigan State, Maryland
2002 Maryland Indiana, Kansas, Oklahoma
2003 Syracuse Kansas, Texas, Marquette,
2004 Connecticut, GT, Duke OK ST
2005 UNC, Illinois, Louisville, MSU
2006 Florida UCLA LSU GMU
2007 Florida, OSU, UCLA, Georgetown
2008 KU, Memphis, UNC, UCLA
2009 UCONN MSU, Villanova, UNC
2010 Duke, Butler, MSU, West Virgina
2011 Conneticut, Butler, VCU, Kentucky
2012 Kentucky, Kansas , Ohio State Louisville
So not really many surprise teams. For the most part the teams you expect to make it make it. Most of those schools are known hoops schools.