Hmm, there were quite a few noteworthy adventure games - Citadel set the mould, Palace of Magic followed it (they play almost identically). Ricochet was an interesting twist on the theme. Castle Quest is a fantastic game - great fun - but somewhat short.
Oh, and who can mention BBC adventure games without saying "Exile"! It'd be interesting to see whether that can run on the emulator - I've had mixed results before. ModelB can run the game fine, but doesn't have a "save state" feature; BeebEm can only run the game with sideways RAM support disabled, which means you get a really small screen.
Along the theme of maze-style games / Boulderdash clones, Ravenskull and Bonecruncher were already mentioned though I never liked those much. Repton was of course the biggest name there, starting from a simple Boulderdash clone and moving on to more serious puzzle solving gameplay, particularly Repton 3 which had at least four expansion packs (of varying quality).
If you like puzzle solving, though, XOR is very satisfying - 15 levels ramping up from series of small puzzles that are easy to solve, to complex levels with a lot of interaction between different puzzles, where you sometimes need to pretty much plan the entire level to win. It's a very pure game, and very satisfying to solve.
Regarding Planetoid vs Defender, Snapper vs Pacman, there were quite a few cases where the official ports of games were substandard, and more dedicated non-cross-platform software houses (mostly Acornsoft, who were bought out by Superior at some point) remade the same games with different names to a higher quality level. Some other examples are Mr Ee (Mr Do) and Killer Gorilla (Donkey Kong). I prefer playing Mr Ee on a BBC emulator to Mr Do on MAME... not sure why, maybe familiarity does come into it though.
Thrust was a good game too - one of the first examples of (reasonably) accurate physics influencing gameplay. Kind of brings me on to Space Pilot in a way, and Deathstar (= Sinistar on other systems, I think).
Hmm, what else... Contraption, Boffin, Elixir, Codename: Droid, Wizzy's Mansion, Thunderstruck, Psycastria, Inertia, Plan B... Magic Mushrooms... I guess I could go on all day reminiscing.
And Twin Kingdom Valley was a great text adventure, I guess that's no good on a handheld though!
The BBC was an incredibly well-designed system for its age, the extensibility was amazing, and the OS seemed top notch. Providing a built-in assembler was a nice touch, and even that had useful features such as support for forwards branches and relocatable code. BBC BASIC was streets ahead of many other BASICs (what's all this GOSUB rubbish?) and I think generally the system was well tailored to homebrew development. Kind of like the GP2X I suppose, in that it didn't necessarily get the attention of the main developers of the time, as the market was relatively small, but those who owned and used BBCs really appreciated the machine.
The same was true of the Archimedes (for which the ARM chip was designed - did anybody here know that ARM originally stood for Acorn RISC Machine?). It was in competition with IBM PCs, but they didn't have the clout to market it worldwide, so it always had a smaller userbase, meaning less software available. But (I'm told) the software that was available was generally of great quality. The Archimedes had a much better quality window system and multitasking capability than its IBM-compatible brethren. I find it really sad that the people who became market leaders out of all this (Intel and Microsoft) were generally peddling lower quality devices and software...
