I focus, now on CIB NES, SNES and N64. Though I also just through random pickups have a pretty bangin' CIB GB/GBC/GBA collection. Nowhere near complete for any of them but I have most of whats worth collecting for them loose (not true of NES and SNES.) Also have an okay Gamecube collection. Aside from that I have massive amounts of PS, Xbox, Sega etc. stuff that I don't really care for and should probably just sell in order to save space. Also have a bunch of old PC games that I should get rid of, but probably won't. A lot of that is early, starry-eyed pick ups from when I was just starting out, lots from in-person auctions (which have since dried up and become harder to win, the fewer common items I am looking for) or dollar a piece or less flea market buys.
When I started out my main goal was to get a complete N64 collection. By this point in time I have enough money tied up in other stuff that if I were to sell it off, I'd have the cash to just buy one. Well, if I did get that done I guess I'd be moving on SNES anyway.