the kree-skrull war?
Although a classic, I've always thought that was "over sold" as being "Great" (But I feel the same about WATCHMEN, sooo ...)
Not sure about "grandiose" but the original Surfer title, with art by the true master - John Buscema, was a classic (though not too deeply set in space).
(of course SILVER SURFER also had a huge run later)
I enjoyed the 2 HERCULES limited series set in space by Bob Layton. '82 and '84. Those were fun.
The GUARDIANS of the GALAXY had a great run for a while in 2008 that was really good -
and if you chose to take a chance on 90's Marvel *shiver* that same title had a long run of issues starting in 1990, but I never read any of those
And of course, if you truly enjoy Starlin's cosmic stuff you have to read DREADSTAR!!! In that series, he even self-stole Thanos back. Well, a 2.0 version of his character anyway.
EDIT -
And oh yeah, Almost forgot
OMEGA MEN.
Loved that DC series