I am this close to reporting you
Accept no substitutes.
If you look through whatever version of the games you buy and you realise that something from the top list is missing, I'd definitely recommend rectifying that immediately.Must have
ME1 - Bring Down The Sky
ME2 - Kasumi - Stolen Memory
ME2 - Zaeed - Price of Revenge
ME2 - Lair of the Shadow Broker
ME2 - Arrival
ME3 - From Ashes
ME3 - Leviathan
ME3 - Omega
ME3 - Citadel
Good, but not compulsory
ME2/ME3 - Genesis 1/2 (This is really cool but only really a valid if you are skipping ME1/ME2 which you really ought not to for a full experience)
ME2 - Firewalker Pack
ME2 - Overlord
ME2 - Normandy Crash Site
ME2 & ME3 - Weapon Packs (these aren't at all necessary but the quality of the weapons are pretty good so if you really want some more variety grab 'em)
Avoid
ME1 - Pinnacle Station (Realllllly not worth it)
ME2 & ME3 - All alternate appearance packs (do not add enough to the game to warrant a price tag, unlike the weapons)