I'm probably in the minority, but I almost never look in the gallery and never download all sorts of gallery unlockers. I'm interested in the game, not the pictures. Gallery pictures/animations add nothing to the gameplay.
I appreciate it when a Dev includes a replay gallery, especially if they also provide the option to unlock it which is nice once you finish the game to see what you may have missed. Likewise, appreciate those who provide a separate gallery unlocker MOD if unlock is not built into the game itself.
I've spent countless hours replaying certain scenes, just to relive the experience and see if I can discover something new, it's interesting how some moments can be just as captivating the tenth time around as they were the first.
A replay gallery should always have all the scenes and events where an H scene happens and you can't get to witness. Take as example Scars of Summer (Not After) that game has some H scenes in free mode that you will never know or see in the gallery unless you go and look for a "All scenes of X route" video or you select an order of right choices.