Coming back to your new game
In the past, when I have played one of our older games and it has been a while, I usually just noticed all of the new features of our games that isn't in that particular game. This is probably a pretty common feeling among developers in general. I can't imagine it's just me.
I put a lot of work into our next game last year and then I went back to finish up and polish the Orc Schism expansion. So I haven't looked at the next game really in months.
Getting back to the game is interesting and a little bizarre feeling. It's similar to rediscovering one of our older games, except it has cool features that don't exist in any of our other games. I keep running into cool things and remembering "Oh, yeah I added that feature already". For example, I ran into a sign that said "Don't touch". I had forgotten that I had already added random signs for various things. It then took me a while to figure out what the sign was referring to. I finally found the hidden stash sitting in plain sight, but is a common object so it's easy to overlook.
This has happened with lots of new features: graveyards, chained traps, levels within levels, full secret levels, lairs, etc.
Depths of Peril, Kivi's Underworld, Din's Curse, Drox Operative, & Zombasite