It's a cliche among comic book fans and the general population. Superman is lame.
Originally I always thought this as well. I always preferred characters that are more limited like Batman or my all-time favorite, Spider-Man.
However recently I've started finding myself enjoying the Man of Steel more and more. I think it's for a simple reason, Superman is a symbol of all that is good in this world. He has so much power at his disposal, even more so than Spider-Man, and it is he that embodies the concept of "great responsibility" when it comes to his "great power". Spider-Man is defined by this statement because he is always forced to struggle with this concept in his life but Superman has come to represent that idea.
Many of my friends criticize Superman as being a figure that they cannot possibly relate to when compared to someone like Batman. In contrast I find it difficult to believe they have anything to relate to a multi-billion dollar orphan who spent his entire life traveling the world to hone his body into the ultimate crime-fighting machine. I feel the idea of Superman as a person always feeling like an outcast amongst society is a theme I am only too painfully aware of. Superman is in some ways, more human than Batman because he's lived his entire life wishing to be accepted and not feared for his power. Batman is quite the opposite, never desiring acceptance and thriving on fear.
Amusingly enough one of my favorite depictions of Superman is his recent appearance in the not too too loved Superman Earth One. I loved this comic for one reason. The reason why he is a reporter. Superman is a being of incredible strength and intellect. Reading and punching bad guys are things that come naturally to him. But being a reporter, writing and telling people of the events that happen around him. That isn't intellect or strength, that is the gift of creativity, which is something you can't just speed read in a book or lift cars to understand. Writing requires an understanding of what readers desire, of what humans desire, and there Superman can learn to understand humans which is a theme that is too familiar with the Last Son of Krypton.
In conclusion, basically what I'm trying to say is. I don't really know why I love Superman, just that he's a character that I'm slowly learning to appreciate more and more.