I'm running 4 players through a fusion of Nocturnum and Delta Green Countdown.
Things I like:
Interesting settings including a monastery in the hills, an offshore oil rig, a college town.
Interesting cast of characters, former green beret/cia guy, immortal observers.
Enough leeway to insert other adventures, easy to substitute baddies.
Things I dislike:
The chain of clues and plot hooks are occasionally tenuous and approach the edge of railroadyness.
D20 conversions are about 50/50. Expect to examine and revise some stats.
Expect to put in a little work smoothing out the rough edges.