Bulk Slash (Saturn).
Its a 3D robot action game, where you can transform between Robot and Fighter modes with the push of a button. Its nicely varied instead of just "Kill all target" scenarios. There is an escort mission and even a bombing run where you have to deliver bombs to certain points in the middle of an aerial mine field without getting shot.
What really makes this game memorable though is the Manageable Intelligent Support System (M.I.S.S.). On every mission there is a female navigator to find. She'll help you out by making targets easier to find and each girl has her own secret bonuses (faster speed, more shielding). They'll get delighted when you get big combos but get pissed when you take hits, and are totally hilarious. Plus each girl has her own fully-animated love ending with the hero.

Too bad this one never left Japan, as its great fun for all.
Video:
PS- My avatar girl is Meticul Flair, my favorite girl from this game.
