MGS quality has definitely fallen, but most overrated franchise ever? No. It dropped 3 classics in a row, then finally fumbled on the 4th, and didn't quite deliver on the 5th. MGS2 is a classic, don't let the initial Raiden haters fool you. That game was still masterful in its own way. Great boss fights and had a shyt ton of fukkery that could be had, plus the VR missions in Substance was great.
MGS 3 is a top tier game. The atmosphere, the design, the story, the soundtrack, the boss fights, the camo and injury system, everything made it feel like you had to work to survive in the jungle while carrying out your mission. Can't praise that game enough. It's truly epic.
The last 2 games haven't helped its legacy much, but it's an iconic, legendary franchise overall and shall be respected as such.
None of those are touching MGS breh. Sonic fell off worse than any franchise listed in this thread and Half-Life would be the only franchise that could compete if 3 ever dropped.