While, in hindsight, Invaders is the trial run before Roy Thomas strikes gold with All Star Squadron, at the time, it blew me away, as a kid.
A super hero team, set during WW2, featuring a whole bunch of heroes I only kinda, sorta knew about: Wait, Namor used to be a good guy before he fought the Fantastic 4?
There were other Human Torches?
Was the Liberty Legion a real thing from the 40's?
It is a bit of a mess, but it is a fun, pulpy mess, that makes decent use of marvel history and attempts to fix and fill in some gaps.
Plus, Frank Robinson's art was so different from most guys drawing for marvel. The heroes looked heroic and bright, but everything else had a gritty, war torn look to it, that just perfectly captured the time period.