Franchises you used to get excited for but don't anymore...

[Zod95]

GTA San Andreas --> GTA IV (less content, worse environment)
Midnight Club II --> III --> IV (worse content, less fan)
TOCA --> GRID (less content, no decent motorsport environment)
Colin McRae --> DiRT (less content, no decent rally environment, worse graphic style)
Soul Calibur III --> IV (worse gameplay)
Rome Total War --> Medieval II (worse gameplay)
Mega Race 2 --> 3 (big LOL to what they did)
MotorStorm Pacific Rift --> Apocalypse (worse environment)
Crysis 1 --> 2 (no military warfare, only aliens)
Sonic Adventure 2 --> Heroes (worse gameplay, worse levels, worse graphic style)
Tony Hawk's Pro Skater 2 --> 3 --> 4 --> Underground (worse levels, worse style, worse game structure)
One Must Fall 2097 --> Battlegrounds (worse content, less content, worse gameplay)
Virtua Tennis 2 --> 3 (worse gameplay, no smooth graphics)

Worse than disappointing sequels, these awesome games didn't have any sequels at all:
This is Football 2005
The Getaway Black Monday
Crashday
Z Steel Soldiers
Destruction Derby Arenas
Vanishing Point
SWAT 4
Smuggler's Run Hostile Territories
Test Drive Eve Of Destruction
Project Gotham Racing 4
Command & Conquer Generals
Homeworld 2
Monaco Grand Prix 2
TrickStyle

If the videogaming industry picked half of these series and did proper sequels, I would be the happiest person in the world!