One mecha RPG game is Armageddon: 2089, which has a main rule book with a busy background, the fluff text in sidbars was 1980s style with green text on black background (but they chose dark green text), the page that describes how to set up a Merc unit has two different dollar amounts for how much your starting funds are, the weapon charts are split so names are on one page and some stats on another, some of the necessary details are so easy to miss (one of the options is 'tech support', without it your targeting software only provides half its bonuses), and most of the mecha in the main rulebook are well outside starting character budgets (starting character budget is $20M for 4 mecha, some of the mecha are $40M each, and one has a pair of weapons that each cost $50M). It is supposed to be D20 compatible, but the mecha are reclassified as Medium so it is difficult to bring it into another D20 game. There is no guideline as to what sort of enemy force should be built based on the strength of the PCs, plus the special abilities of the vehicles (and overall design line) is all custom to the game system as well.
It does have some nice ideas though about resistant armor but easy mechanics, capacitors just total extra power from the engine instead of anything fancier, though if you forget to mount the anchoring spikes your artillery Mech will fall over.
Fun quote from the book:
"I need fire support, air support, and tech support, and I need it now!"