I agree if you have 3 good friends ODST is the best. Solo, it is impossible to get the achievements.

Actually it's possible to get a lot of achievements solo given that you know what you're doing and are fairly skilled enough. The only one that is probably impossible to solo is the one vidmaster on the final level. That was a real bitch.

Respect is due. I am fairly skilled but no pro.

Skill is necessary for execution. But it won't carry you to victory.

Method & Skill is the key to success.

That's how I helped people with endure. We would get on Lost Platoon and you needed at least 1 skilled player on the chopper to slaughter everything and smart enough to not get killed. We barricaded the stairs with crates and a warthog. 1 person with an SMG to take out them flying buggers, one person with laser to remove the wraiths, and one person to make sure no one gets killed, but this guy usually can just hide in a corner given that everything goes smoothly. He usually ends up stockpiling extra choppers under the main stairs in case the main chopper driver gets killed.