Should prequels for trilogies be made?

Should prequels for trilogies be made? Are they a cash grab or valid forms of gaming? 

It seems inevitable given the success of Gears of War 3 that there will be another game in the series. It's too good an intellectual property to just let things end because the cash cow can surely be milked some more.

Despite things ending very well for Sera and the few COG soldiers left in the final campaign, there's still a lot of baggage running in between the ears of Marcus Fenix and it would seem a fourth Gears game could mine some of that baggage.  And that baggage is Emergence Day. The day the grubs clambered out from holes and burrows and caverns to start a devasting war.

So the question is, will Gears of War 4 be a prequel?

The second question then becomes should it really be a sequel? Dos the quality of the game suffer? Should video games be prequels?

Look at this list, what games stand out? Deus Ex, Prince of Persia: The Forgotten Sands? Hardly games that are household names but each servicing their little corner of the world well enough. Perfect Dark Zero was a handy enough game... right? Perhaps not enough of a success to make a fourth Gears game a prequel?

There is an elephant in the room however and that's a wee game called Halo: Reach.

Let's take a look at that game. It was the story of the beginning of the end for a Planet, with new characters and a plot that did its best to tie the plot into a very well established game canon and mythos. Halo: Reach can be considered a successful prequel.

So Bungie Studios made the prequel work following the conclusion of an epic trilogy story arc. And perhaps they had to because Microsoft was moving on with the Halo series regardless so if Bungie had one game left to make in the Halo series, a prequel was ideal as the game makers didn't need to come up with a three game story arc.

Halo: Reach is the stand out prequel that worked and given that Gears of War is on a comparable scale of success and commercialism with the Halo franchise, it seems reasonable that Gears would follow Halo's path.

And if Gears does follow that path, one can only imagine how that might inspire the makers of Mass Effect. Scared much?

Extra for Experts: I actually doubt ME4 will be a prequel as Mike Gamble has said to keep your saved games from ME3 - it would be paradoxical (is that a word?) if decisions already made influenced the game play of a prequel.

Extra for Experts 2: Who really cares about the cash grab arguments - all games are cash grabs - programmers and companies that employ programmers do it to make money. Sequels are just obvious cash grabs.