[[[ ---> Critical Mass <--- ]]]
If FTL is the Enterprise, then this is an X-Wing. In some ways, its a polar opposite, but somehow is scratches a very similar itch for me.
It's still got perma-death, but is structured as an unending march of increasingly difficult randomly generated missions, rather than one long mission with a definite end. You may get a medal or a promotion after each mission depending on performance. You can sometimes fail a mission and still survive (via fleeing/ejecting).
It's a bit pricy at $20, but there's a free demo.
Something to do once you've got 100% completion on your FTL achievements while you wait for the next update or cool mod to come out.