I was watching a bit of Dark Souls 3 stream on Twitch.tv. (Spoilers, beware:) I was shocked when the player (Peeve, in case anyone wonders) ran into a rehashed NPC form the original Dark Souls named 'Siegward of Catarina'. Boasting similar character traits as our trusty Siegmeyer from the original; wearing the same suit of armor and weapons, I suspect the same voice actor, and even opened with: "Hm... Hmmm.. Oh!". I was a little bit disgusted by this. First of all because I'm a Dark Souls 1 fanboy, but mostly because of the developers deliberate decision to pretty much copy an old loved character which I can only assume is for fanservice. And I, as a fan, don't really like it at all!
On the other hand there was Metal Gear Solid 4, where we (Spoiler:) took control of Rex and fought smurfing Ray! I totally did not see that coming and it was awesome. Going back to this place was fan service too, but it got so over the top and unconventional that I really liked it!
TLDR: what are some fanservice/throwbacks in sequels that you liked/disliked?