When did pokemon start going downhill for you? For me it was after gen 3. The only reason gen 4 sold better wasn't because they were better games but because it benefitted from the DS having a larger install base than the GBA.

Gen 4: Played worse than gen 3
Was really slow gameplay wise
Champion was a cliche blond fuckbitch instead of a cool Millionaire with a steel cock
Gen 4 had shittier pokemon designs.

I could go on.