-The original Dragonlance modules.
The problem with that was that we started back when everyone was in college, and then never quite got the end (DL12) before everyone went off to University. In fact I don't think TSR had quite finished producing the modules. Plus in the original game we used the pre-gen characters and nobody really cared about them.
I've tried twice more to run all the way to some sort of conclusion. Once as a PBeM, but being a PBeM it took years to get anywhere and then fell apart. Once using RQ rules instead. The problem being with both these attempts is that I'd stripped away as much of the pre-gen and railroading stuff as I could and ended up with something that was too much work for me!
-The Enemy Within campaign (Warhammer FRP)
Same as above (we must have run them consecutively or something, I can't recall!). Once again, everyone had moved on to different lives before the games company had finished producing the adventures. As I recall we got to Power Behind the Throne but didn't finish that book. The next two installments were quite disappointing anyway.
I've also had several stabs at running a Shadowrun campaign (using the pre-bought adventures) but came to the conclusions that (a) the pre-bought adventures are largely full of holes and/or railroading, (b) the game system* is a pain and (c) some people like very wierd and disturbing character concepts in Shadowrun!
(*) 1st and 2nd Ed. Owned 3rd, never played it, so haven't bothered with 4th.
I've had loads of games/adventures that I've wanted to run but couldn't because I couldn't find players interested. Horror on the Orient Express was a biggy. I'm still hoping to run my Arcana Unearthed game one day, too