Coming back to this post because I really like games that let you walk around big vehicles, especially ones piloted by players
There's Guns of Icarus, a multiplayer Steampunk airship combat game where teams of 4 have to work together to take down other ships. I only played this one a little bit and it's ******* DEAD
Then Blackwake, which was a lot better and I put quite a few hours into. Generally teams are split between a few ships of varying sizes, with some crewed by up to 16 people. With so many players, duties would be split up between spotting, patching up holes, pumping water, putting out fire, loading the guns and delivering ammo, etc. Having 12 people run the guns on the port side and annihilating an enemy ship was the coolest **** ever. It is also ******* DEAD
And this one barely gets a pass but the Halo 4 mission "Reclaimer" takes place on top of a Mammoth, a giant fuckoff vehicle equipped with turrets, power weapons, a bunch of marines, and smaller vehicles, which makes it one of my favorite Halo levels even though the game sucks and is ******* DEAD