The reason why people hate Reach is either because
1. They suck at the game, since it puts all players on common ground and eliminates the "skill" required to get kills by adding bloom. Like it or not, the game is harder, since good players don't get rewarded for having skill
or
2. The game was a HUGE, HUGE freaking promise for the franchise, but it failed miserably and made the Halo community die out in less than 2 years. If Halo 4 fails, oh boy.
Reach wasn't easier than Halo 3. Reach relied waaay too much in team shooting, which killed the fun 1v1s in plenty of games, which also contributed to boost Call of Duty's and Battlefield's popularity, since those games do reward good players both in 1v1 encounters and team shooting (suppressing or whatever)
My point, Halo 3 was easier than Reach. Deal with it.