I do have a case of bed head right now. But my hair is fine normally.
RE4 took me 28 hours (first run, Normal), 16 (New Game+), 9 (Chicago Typewriter run), and 22 (Pro Mode). That was all in the GC version.
When that memory card got corrupted, I bought the Wii version and sunk many hours into that one as well. 19 hours (Normal), 17 (Pro), then 10 (Pro NG+). And then there are the hours I spent on the extra content as well, in order to unlock everything.
RE4 was a LONG game, and for me it was even longer than it was for the average player because I spent a lot of time taking in the environments, planning strategies, and looking for all the secrets that I could possibly find. Looking back, that game was a real fucking indulgence.
Interestingly enough, RE5 was a game where the low-ball estimate (8-10 hours) was just about right for me, but that game was much less rewarding than RE4 so as a player I wasn't inclined to spend more time than necessary to complete the main campaign. I haven't read any of the in-depth impressions of RE: Revelations, but if the press happen to say that it's more in line with RE5 than RE4 in terms of content, then that might go against my reasoning for gauging the game's length based on the high-ball estimate.