Quite a few games that have come out in the past few years there have been 3 major survival game modes: Horde, Firefight, and **** Zombies. Which one do you, the people, think is the most fun, has the most replay value, and should be included in later sequels.
Firefight really disappointed me in terms of what I expected, which sucks cause I favor Halo to Gears and occasionally CoD. It's not even the lack of customization which they feel they need to include in Reach, but the bores I attain from fighting off waves of covenant who do nothing new. Same old covenant noobs I pwn relentlessly in each campaign installment. So I'd have to say Horde and a Zombie mode are necessary for future installments of the Gears' or CoD franchises.
They are always fun distractions the first couple times you do them, but soon they just lose their charm, and even different maps make minimal difference. **** Zombies is by far the best of these, because it allows you to rebuild defenses, and because of the random element of weapon crate. It also has one difficulty setting IIRC, which gives a single standard to base players on, making it challenging, but fun to try to beat old records.
^This Although I enjoyed firefight more than horde and I'm hoping there will be "forgable" firefight maps in reach, if so then firefight will be my personal favorite of the 3.
**** Zombies was fun until the Last map, it just got rediculous by then, adding in stupid and unecessary things.