I don't find the Grado SR225 fatiguing. I like their forward sound and often listen to them for hours (>5) at a time with great enjoyment. Their clarity is what keeps them from being fatiguing for me. Within the Grado family, I'm definitely a "bowl pad" man, for comfort (it makes them more like a circumaural phone, which I greatly prefer) and sonic (the clarity is greater and spectral balance more "right" to my ears with the bowls) reasons.
Another "fun" phone which I own is the AKG K240S. The bass is forward on these, with the mids recessed a bit behind that, and the highs recessed a little more. They have an overall sonic flavor somewhere between the Grado SR225 and the Senn HD580. They've got good impact where the music contains it and a capacity for refinement where the music provides that. An amp as modest as a Headsave Go-Vibe will drive them quite well, but I enjoy them unamped also. And they are "fun". In fact, they are often dubbed a "groovalizer", as distinguished from an analyzer. They are also quite detailed and give what I consider to be a definitely Hi-Fi, but not analytically accurate, sound.
I'm currently buying a pair of AKG K-501s to get the "accurate" sound.
So, you've got two "fun" phones to look into, the Grado SR225 which is more forward in the highs and the AKG K240S which is more forward in the lows. Both really fine cans, IMO, and good for a broad spectrum of music. I don't buy into the "Grados are just for rock" pidgeon-hole. I very much enjoy electronica, jazz and classical on my Grados and AKGs as well as rippin' rock.