I believe Daron Malakian co wrote it all with Serj Tankian. The stuff he has written by himself hasnt been aweful, some has been pretty good but its all written on piano and he fits the music to go around the piano, which is fine, but i dont think it works with all the songs.
Well i couldn't push myself to listen after the 6th bad song anymore, so maybe it was just awful selection by me, but i tried the most popular ones

Of course piano is fine, i play piano myself, but some of the Tankian songs are so simple, primitive and/or with bad lyrics, that even i could match such level. Like 'baby oh baby, i miss you, la la la la.'