Maybe you can mention what systems were released during the 4th gen, as it would save google searching - the same applies to any topic about a 'gen' in Legacy Platforms. If you meant the one that included the TG-16, Neo Geo, Sega Genesis and Super Nintendo, then make sure you check out MechWarrior 3050. As far as what I remember most about it from the time - it was an overhead/to the side 3rd-person perspective. It was somewhat Strategy-heavy, though I mainly liked how the mech controlled and how you could walk around causing destruction, albeit on a fairly small scale.
Mecha games from the 4th generation? The only game that I have anywhere close is Super Godzilla. MechaGodzilla is in the game. And Rise of the robots for the Super Nintendo.
But games like Mechassault, Amoured Core. were not until later generations.
Mega Man X series on the Super Nintendo is the closest to "Mecha" There was a Super Robot Wars game on the Super Famicom but it did not make it to North America. Super Famicom is the best bet for "Mecha" type games.
Super Famicom has 1400 Games in it's library from 1990-2000 While the Super Nintendo only has 784 ish games. 1991-1997. So for Mecha games Super Famicom is your best bet.