You don't need new monitors. You need a new singer and guitarist.
Overall, the mix really isn't that bad. Drums are nice and tight, EQ'd well. Bass has a nice punch (though it could be louder).
But the lead vocal and lead guitar performances need a lot of work. Vocalist is painfully flat during the chorus, and lacks soul throughout the song. The guitar work is mechanical and the notes are not correct, during the famous (and repetitive) opening passage. Guitar also needs some overdrive.
If this is intended as a demo to get club/bar work, do yourself a favor and re-cut the vocals and guitar from scratch -- after rehearsing for a few hours to the original record.
(Sorry to be harsh. I post mp3s on here occasionally and would much rather get honest feedback than have someone blow smoke up my ass.)