I've spent as much spare time as I've been able playing Bob Smith's superb Boulderdash clone for the 16KB Sinclair ZX81 called Boulder Logic. It's a fairly predictable affair if you're familiar with this type of game: collect the Diamonds, aviod the rocks and roamers and find the exit in time before the oxygen runs out. What it proves is that a good game is a good game is a good game, regardless of the platform it is running on. Saying that, there is some skill in getting playability out of Sinclair's binary beast, so well done for Bob for that, following up his excellent Virus game released last year.
The most promising thing about this production is that it's not finished yet, but it may be downloaded at this link: http://www.bobs-stuff.co.uk/extras/boulderl_wip.zip - or check out Bob's site (http://www.bobs-stuff.co.uk/) to see his other wares. I personally can't wait for this one to be finished.