One of the most underappreciated games in the RPG and mech world's gotta be Zone of the Enders and Zone of the Enders: The 2nd Runner.  Both of these games were some of the best mech games I ever had the pleasure of playing.  i remember kickin back in my dorm room (skippin a few classes) and playin Z.O.E. : the 2nd Runner.  I love these games man!  Dingo was bada** on the sequel mayn...gotta love it!