Well...my own tastes are a tad bit more vintage....
One of my all time fav's is Blade Runner...and I mean the original, not the stinkin' director's cut.
Also still enjoy Dune...the 1984 version directed by David Lynch. I remember a lot of folks got upset with this movie when it came out because "it wasn't like the book", but then, like LOTR I never read the book, so I loved the movie...still do!
Ok...a tad cheesy in the fx department by today's standards, but I still love Logan's Run...now there's one I'd love to see re-made with modern tech!
The 1972 "Silent Running", while more than a tad depressing, it still worth the occasional night on the couch with a bucket of popcorn.
Also good for the occasional bucket of popcorn, while not exactly a space epic, I always loved the 1973 classic "Westworld". Yul Brynner was just way too cool

.
Oh...and speaking of cheesy...ok...I admit it...I need help. Yes, I LOVE "Howard The Duck"! I've watched that movie so many times I've actually worn out the VHS tape, LOL!
Not sure any of those
really qualify as under-rated, but there we go :-)