By this do you mean a somewhat similar game but with better gameplay?
HAHAHAHAHAHAHAHA... no.
Fallout's actual combat mechanics were a junky mess, and while the character design was praised as unique and revolutionary at the time (most likely because of the expansive freeform skill system; the vast majority of cRPGs even up to now have been class-based), in reality SPECIAL was actually pretty damned awkward and littered with seldom-used skills and near-useless perks. The fact that you could control a squad was hardly even a plus, since that control was limited and their AI was horrible. Yet still, the combat was fun, and it had style too thanks to the great death animations.
Don't get me wrong: I'm an original Fallout fan. My Internet presence was slathered in animated Vault Boy avatars and sundry for years post-1997, and I've played through both games many, many times. I've sunk hundreds of hours into New Vegas. Nonetheless, Underrail's actual character customization and gameplay/combat mechanics are far superior to Fallout's.
Where Fallout shines is in its characterization, writing, and C&C. Underrail shines in its gameplay. The two are about equal in the atmosphere department.
If the strengths of the two were to be combined, you'd have the truly ultimate cRPG on your hands, unless you're the sort of person who requires fast travel and world maps I suppose.