Operation Anchorage is really short but the gear is really cool and the Cliffs part is really fun. Broken Steel is pretty boring at first(when i went thru the train station part it was hilarious as I used science skill+ ghoul mask to make it so I didnt have to fight any and i could just sit and watch the fights) Point Lookout is the biggest by far and yea its like the Wasteland it has a bunch of side quests and quests that arent even documented(like activating the lighthouse) its pretty cool as theres so much to do. and Ive never played Zeta so no comments there. The Pitt is actually really fun and I like the two-sides system
Zeta probably has the coolest gear, Anchorage is meh. There is the stealthsuit, but the gauss rifle can not be fixed unless you go to a vendor. Pitt has the best weapons by far. Point Lookout is probably the best all around.