OpenTyrian - The Best DOS Shoot’em Up - Now for Windows XP/...
Note: 11 of this post’s 15 links are now broken — mostly dead 2008–2013 feed-syndication infrastructure (FeedBurner, Gawker, AOL’s old blog network, Pheedo, Yahoo Pipes). Left as originally published.
I remember playing this old DOS game on a mate’s PC.
Need to download the Nintendo DS version :)
Arguably the best DOS-based shoot-em up in my opinion, Tyrian is now available for gamers on Windows, Mac OS X, Linux (and Nintendo DS, PSP, even Wii!), thanks to the dedicated efforts of the OpenTyrian team who modified the source code to use the cross-platform SDL libraries and of course, Jason Emery, who graciously offered Tyrian as freeware back in 2004.
Installation for Windows users is fuss free : Just grab the pre-compiled Win32 version from the OpenTyrian forums (direct link), the SDL libraries - both SDL and SDL_NET (look under Runtime Libraries) and the original Tyrian 2.1 data files from the OpenTyrian site and unzip them into the same folder in the following sequence : data files, OpenTyrian, SDL, then double-click Tyrian.exe and enjoy!
I don’t think I need to go into how good Tyrian is : old-time shoot’em up fans should already know this classic which comes complete with fully upgradable ships, weapons and equipment, retro tracker-ish music and a storyline to boot (via datacubes collected within missions) while newer fans of genre should not miss this definitive icon of DOS shoot-em up history.
Datacubes - one of the pioneering forms of in-game advertising, courtesy of EPIC MegaGames 
To toggle full screen mode, go to the OpenTyrian option in the main menu and set it from there. You might also want to set the game speed under Options (press Esc in-mission).
Download and play OpenTyrian.