Bungie summed it up best, halo 1 and 2 are 30 seconds of fun repeated over and over again. From start to finish you'll be doing the exact same activities with little to no variation. RE 4 is always throwing new things at you whether it's new enemies, puzzles, or environments. From start to finish the player experiences one gorgeous set piece after another. Driving the scorpion tank in halo is closest thing I can think of as a stand out sequence while in RE 4 you've got the boat battle, the el gigante boss battle, the mine cart chase, the fire room, the wolverine cage, the maze, the castle, the secrete lab, an sequence where you fight side by side with a fricking helicopter, the fight against the right hand man, the Kruasher boss fight. If you even try and compare halo to RE 4 when it comes to the single player experience then you've obviously never played RE 4 or at least never played RE 4 for more then five minutes.