Wow, I am amazed to see so many replies!
Again thanks to everyone who has taken the time and effort to give me ideas.
Whatever I choose, it would be relatively simple and certainly not a commercial-standard game. I like to think I can write something that can hold its own with most of the decent PD games. Perhaps something good you'd sometimes get off a magazine coverdisk.
So for this reason, I think a strategy game, a racing game and things like that are probably beyond my scope at the moment. Likewise, SNES Mode 7-like graphical effects would be too challenging technically for me, and probably not easy in Blitz Basic either. However, the 'infinite runner' style is something I have thought about, perhaps a more conventional 2D side-scrolling affair but it is an option for sure.
One of my favourites so far is certainly Door Door. As idrougge says, the graphics certainly contribute to its charm and it's probably hard to capture that quirkiness and character, but the concept itself is quite cute and is probably one of the politest games I've ever seen (I mean, holding the door open for someone...!). It's got potential, that one. That would also cover the suggestion of an arcadey single-screen platformer (and you could throw in a two-player mode without much bother). Thanks to idrougge for this idea.
I'd also like to thank Selur for posting the Spectrum link - I haven't watched it all yet but this has triggered something for me (I have a Speccy +2 under my desk with a DivMMC attached so you'd think I wouldn't need a trigger). There's a game released in 2008 called Rallybug which I really like and which I've now been reminded of. It's essentially a one-way-scrolling platformer where you control a car, and collect letters to guess a six-letter word hangman-style at the end of a level (!). It's better than I make it sound
(EDIT: This video doesn't have this element and has flags instead of letters to pick up)
[ Show youtube player ]
So, current games under serious consideration are:
- Super Crate Box-style platformer (with additional multiplayer)
- 2D Infinite Runner style (Canabalt-style?)
- A game using the Door Door concept
- A game using the Rallybug concept
Feel free to post others still