The Pentium -> Core2Duo was a great era for intel, but I feel like ever since then they've started a decline in both price/value proposition as well as just general hardware.
The i-series was arguably pretty good for gaming, but then they started exploiting that position by having relatively poor price-to-performance, thinking they wouldn't have any competition.. and they kept the 'we are winning' mindset even while AMD was hot on their heels.