I'll be having some of these:
Chuckie Egg (BBC)
Mentioned it before, but this is my absolute platforming zen. Straightforward goals and pinpoint responsiveness are my best guess behind this being the case, but it just puts me in a state of total interaction with whatever machine I'm playing it on. Got it for Christmas the same one I got my BBC and it's been a staple feature at my 'rents place since going back to visit every year.
Repton 3 (BBC)
Another Beeb game I got that same Christmas, and really the pinnacle of the series. The re-labels don't really count (same game, different graphics, different puzzles) and, while Repton Infinity was decent, the game was a far more complex beast by that stage. Repton 3 was 'pure' Repton at its best.
Stryker's Run (BBC)
Doesn't really need an explanation from me (does it?) apart from the fact that I believe this was another 'un I was gifted for Christmas at some stage.
Sonic (Mega Drive/Master System)
Sticking these both in the same bag. Sonic on the Mega Drive probably offers my fondest memory of Christmas as I got both the console and machine around '92 and consequently played it for the entire day. As for Sonic on the Master System, one of my cousins owned it and we played it (and Sonic 2) on a few Christmas Eves back in the day.
Alex Kidd (Master System)
Another Master System game owned by my cousin and something that was a massive feature of that '92 Christmas due to the fact that I asked for - and thought I was getting - a Master System that year (sneaky family). Sadly, I've never actually completed it, so perhaps this year.
Mega Bomberman (Mega Drive)
Another year, another game for Christmas. This time it was Mega Bomberman which I was ridiculously excited about being as it was the first Bomberman on a Sega console (something that made me incredibly jealous of SNES owners previously). Played many, many battle games with my brother that day.
Christmas NiGHTS (Saturn)
Can't really have Christmas without this game, can you? Never fails to emanate a basking glow of Christmas every time I drop the disc in and boot up ol' faithful.
Last Bronx (Saturn)
Something my brother picked up just before Christmas one year and turned out to be surprisingly good. Since then, it's been fished out of the cupboard on more than one occasion around the end of the year.
Obviously I'll also be playing a bunch of other things (like the collection of PS2 games that I haven't seen for about a year) and there are non-mentioned games that have great Christmas memories for me too, but I really had to single these guys out.
Happy holidays, people.
Mario during the day when everything's happy and cheery, then in the evening when it's gets dark I'll stick Goldeneye on and start shooting people. 
Can't have Christmas without some James Bond in there somewhere. Probably take Goldeneye round to my mate's on Boxing Day
