(after spending a few minutes trying to write this im just going to keep it simple)
Morrowind:
Pros:atmosphere,gives a hefty sense of accomplishment(when you finally find the place you where told vague directions to,can easily be modded to about 2005 graphics w/mods
Cons: clunky ui/controls(the controls can be changed),early-game is slow(literally)
Fallout 1:
Pros:very small file size(w/dosbox and a bit of tinkering can easily fit on a pendrive)
Cons:requires running through dosbox,very old,turned-based
Neverwinter Nights Diamond:
Pros

&D
Neut: Graphics are meh
Cons

ld,clunky control/camera(at first)
Daggerfall:
Pros:another very small file.
Cons:Very and i mean -very- clunky combat controls,very old
I tend to lean more towards older western rpgs so the biggest problem for most of these will be graphics and for some control schemes(for the really old ones) but beyond that they usually can keep you busy for a few hours(or a few hundred).
If you want any in-depth details about any of these just ask o/