Hmm, the abrupt cancellation of the 3.5e Ravenloft Gazetteer line was one of them. I genuinely loved those books, and aside from an interesting 'metaplot' and narrator, they gave a lot of depth, verisimilitude, and atmosphere to a setting that had often been a series of loosely-connected adventure sites. I did have hopes that they'd eventually go up on DMGuild and maybe the original creators would consider completing the series, but VRGtR took the whole setting philosophy in the 100% opposite direction to the Gazetteers (one I personally don't care for), and while the books were on DMGuild for a little while, they got suddenly yanked a while back, and as far as i know there's never been any explanation as to why. I occasionally harbour dark and probably overly-paranoid suspicions that WotC want to keep the new 5e incarnation of Ravenloft front and centre and don't WANT the Gazetteers competing.
The other is probably Mutants and Masterminds. Yes, it's still around, but the line is basically a shambling zombie at the moment with very little life in it. I discovered M&M at the very end of its 2e 'golden age' and got right into it. But while there was a lot to like about the 3e system, it could have used a little more playtesting in a few places, and the sales model that Green Ronin used for it (lots of tiny $5 PDFs which maybe get released later as a compiled hardback) was extremely corrosive to the quality of the product line, and left a very bad taste in the mouth from a value-for-money point of view. And these days, Green Ronin is much more interested in its licenced properties and the AGE system, and M&M really just stumbles on as a neglected afterthought. Very few people seem to play it these days - back in the 2e era it was everywhere.
