A long-running series of danmaku(lit. 'curtain fire', more commonly referred to as bullet hell) shooters; the Touhou games are programmed, scored, designed, and written by one guy: ZUN, aka Team Shanghai Alice.
The first five games were on the PC98, and are generally considered worth passing up on.
The good stuff began when the team that made the PC98 games dissolved, and ZUN set out on his own.
This was the result.
Embodiment of Scarlet Devil
was the first game of the 'ZUN' Touhous, created for the PC.
Long-term series protagonist Reimu Hakurei and black magic specialist Marisa Kirisame set out to investigate a red mansion that appears at night, and have to defeat its undead mistress: Remilia Scarlet.
Touhou 06 not only maintains a devout following, but it also introduced many characters who still remain popular today, such as Hong Meiling, Flandre Scarlet, and the idiotic yet lovable fairy named Cirno.
Reimu and Marisa are in nearly every game, with an assortment of other characters of new and old origins showing up to help out from time to time. Reimu uses homing shots consisting of spiritual wards, Marisa lays waste to everything with hi-powered, focused black magic lasers.
Here's a good summary of Touhou 6's events:
What separates Touhou from other shmups, among many other things, are the bosses using what's known as Spell Cards:
When a boss' life is almost spent, they break out ridiculously powerful attacks.
The only way to stop them are to finish them off.
There's also the Extra Stages, a series tradition, where things get realllly crazy.
Touhou is first and foremost a shmup series, but the popularity of the series(namely for the wild and varied cast of characters) has gone so far beyond that to the point that some fans haven't even played the games they're based on.
The entry point for some is the ridiculous amounts of fan art and fan works the series has lead to, such as the insane videos created by IOSYS(a doujin remix group).
(^Another EoSD tribute.)
IOSYS mostly make vids based on the music from the series.
In addition, you can find all kinds of awesome remixes if you know where to look.
Since Touhou 06, there have been seven
additional games, not counting the fanmade offshoots such as Touhou 12.3 and such. Quality and appeal may vary, but one thing is for sure: the production values continue to improve along the way.
The design of my favorite, Touhou 08: Imperishable Night, is up there with my favorite mainstream shmups.
You can find information and free demos of all the mainline Touhou games at The Touhou Wiki
. If you own the full games, you can also download translation patches for all of them from the Touhou wiki.
Quality may vary, but they tend to at least cover the jist of the plots(vague as they are).
The 13th Touhou Game, Ten Desires, recently made a demo available.
Good luck. If you can't get it from the many broken mirrors, hit one of us up.
Several fans have created mirrors of their own, we can surely get you one.