Oh, myself, I wasn't complaining. I'll probably consider some of the overlaps (like banshee & groaning spirit, or both shadow demons) to be "lesser" and "greater" versions... Same thing for death and demonic knights. (Actually, since death knight is a template, it could be applied on a demonic knight, couldn't it ?).
Other overlaps don't bother me in the slightiest, because I don't plan on using either version at all (no use for giants in the wood).
In theory, I would prefer overlaps to be reprints of the same, for the sake of consistency, but even intra-WotC this isn't made (compare the Genasi in Monsters of Faerûn to those in the FRCS); and sometimes a new variant is better liked (for example, I prefer the Seas of Blood Leviathan to the MM2 one).
In fact, if there are things that irk me in the MM2, it's rather that it has enforced the stupid "beast have Int score of 1 or 2" (what the point of having both Animal and Beast, then ? A simple "beast have Int score below 6" would have obsoleted much less material, beginning with the Monster Manual 1 !); and the unexplainable policy about player options. There's less than half a dozen ECL below 5, in the usable range; and plentiful unplayable critters like avolakia (!) or Loxo (!!) with ECLs, I even saw an ECL above 30 (!!!), yet no ECL for more reasonnable creatures like sylph or, why not, boggle or nimblewrights. That's be like providing an ECL for the Rast and the Tarrasque, but not for the Azer in the MM1.
Also, there's a note about using fire bat as improved familiar, but none for other decent candidats like ash rat, grimalkin or phase wasp.
That and silly CRs (fiendwurm is CR 18, not 28. Compare the challenge posed by a fiendwurm to a party, and that posed by a solar (CR 19)...).
