I took a quick read of the 4th edition Player's Handbook last night, and looked at a few more reviews online.
From a comment by rentagurkha at a review by Chris Pramas:
D&D is inspired by, and should be able to feel like, the works of Lieber, Howard, Burroughs, Vance, Tolkien, and Moorcock, among others.
That's the big issue so far for me, I think. This edition of D&D doesn't feel like it's inspired by them, but rather by the computer-based RPGs that were themselves inspired by D&D.
Some of this is game mechanics (the Vance-inspired spells are gone, as are the Moorcock-inspired alignments). Some of this is just an instinctive feel - AD&D always had this 70s/80s vibe to it. This edition seems meant to appeal to the folks who think Conan started with the Schwarzenegger movies, and would criticize Elric as being a ripoff of Drizzt.
Will I use 4th Edition? It depends. If there's enough people around to start a new campaign (and now that I'm near the university, that's likely), and that's what they want to play, then sure. Though it doesn't really have the same feel, it looks like it could be a fun tactical combat game. (On the other hand, I wouldn't be at all surprised if 4th Edition turns out to be the RPG equivalent of Windows Vista.) If it's totally up to me, I'd rather use a classless, more freeform system like FUDGE or FATE, and a non-fantasy setting.
2 years ago