I don't know why it's happening, but I've found that if I back out once the game has begun trying to connect me to one of the 20 matches it initially finds, I'm able to get into a game once I try again.
It may be blind luck, but ... it's seemed to consistently work (and if nothing else, it's better than just sitting about).
I've also found that people bail rather quickly from games. I finally got into a horde game where we had 4 people going into waves in the 30s, but it didn't last much beyond that.
Because of that, and that people may be focused on versus at this point, it might be worthwhile finding a group of people to play with on a Web site, or waiting until more people have started playing horde and beast modes. I know that's what I'm planning on doing this weekend.
Fortifications
Barrier
These are used to slow or damage enemies, and can be a handy way to block off paths into your defended area. Upgrades give them additional longevity and damage-dealing abilities.
Decoy
These are used to draw enemy fire. Upgrades give decoys more health, and the final upgrade gives them explosives that detonate upon their death.
Sentry
The sentry is an automated turret that does low damage. When fully upgraded, they can stun an enemy with their fire.
Turret
A turret is a player-controlled fixed weapon capable of heavy damage. Upgrades give them increased range, damage abilities, and heavier armor for the protection of the user.
Silverback
This is a heavy mech piloted by a player.
General Upgrade Information
Upgrades can only be performed between rounds, and require that you have both the necessary amount of cash and the appropriate level. Be aware that some levels do not give you actual upgrades, but instead affect your ability to repair your fortifications.
Upgrades are not shared between players. In your example, only you can use the barriers, but I believe all players can repair them.
Upgrades are persistent between rounds, and only disappear when destroyed.
For more information, such as precise costs of fortification upgrades, see the source link: Gears of War 3 Fortifications
Best Answer
At least for me, the answer is definitely no. The game throws way too many enemies at you for you to be able to have success on your own. I can't imagine surviving the first boss wave (wave 10) on my own, when it throws multiple Reavers, Berserkers, or a Bromak (sp) at you.
It would be cool if they made a version that could be played by yourself, but as it stands today you need a group to hope to complete all 50 waves.