I do not like all music that gets called rock, but for the stuff that I do like, speed, energy, and some emotion in the singers voice (assuming its not an instrumental) are the elements I enjoy most. A lot of toher types of music can offer the same things, and those are not the only criteria that affect if I like a song, but regarding rock and metal, I think those are the main factors for me.
whichever subgenre you like and why will suffice as an answer
Perhaps including a mix of subgenres I like and a few I'm more ambivalent toward will be more informative. When looking at music I like as a whole, lyrics and the vocalist are the most important aspect - I need to feel something when I listen to at least one or the other, and the voice has to be one that does not bother me. After that, an artistic quality to the music or vocals is something that has a positive effect on my listening experience (its hard to describe, and artistic may not be the best word, but its a sense of the artist truely expressing their creativity and vision through the combination of music, lyrics and vocals (this is a sense that I usually only get from more experimental music - stuff that blurs genres or goes into uncharted teritory musically)
Soft Rock -I like some of it, but musically It usually does not do much for me. The stuff I do like is because of lyrics and or a good vocalist.
Indie Rock - This is a genre of rock tthat in general does not appeal to me, the music seldom has enough energy or emotion to appeal to me on a musical level and its even rarer to hear a vocalist for an indie band that I like (I suspect a lot of indie vocalists and songwriters ate xxTx types, but thats just a guess based on the lack of emotion I feel from their songs and lyrics). It might be a subconscious to put any rock music I find to be bland and uninspired into "indie", so its possible there may be some Indie bands I like but don't know they are indie.
Pop-Rock (Britney, Lady GaGa) - Some of it is quite catchy. Not the type of stuff I'd go buy a CD of, but it usually has an energy level that can keep me listenign for a song or two.
Old School Hard Rock/Metal (Iron Maiden, Ozzy, Dio, Judas Priest) - This is the stuff I grew up listening to, and where my main description at the top of this post applies to. Tends to be fast paced, high energy music often with interesting lyrics.
Progressive Rock/Metal (Blind Guardian, Echoes of Eternity, Dream Theater, Kamelot) - I like some of the lyrics and vocals, but in spite of the music being a good pace, I find most of it does very little for me.
Power Metal (Gamma Ray, Hammerfall, Elvenking, Edguy, Alestorm) - Very high energy metal. In some ways, its the evolution of 80s speed metal, but with a lot less anger and aggression. Some of it is cheerful, some inspirational, some just for fun. Good Power metal should impart some of its energy to you - I find it great for improving my typing rate as well as good music to excercise to.
Gothic Rock and Metal (Within Temptation, Sirenia, Beseech, Krypteria, Elis, Delain, Xandria) - This is what I listen to the most often these days. Both the music and lyrics tend to convey a strong emotional component (Most of the time, I can feel the emotion from both the vocal tones and the music itself). This is music I beleive to made by and for INFx types - of all music types, this is the one I relate to the most.
Symphonic Rock and Metal (Epica, Therion, Trans-Siberian Orchestra) - I like the combination of classical instruments with hard rock and metal. The vocals and lyrics of these types of groups usually appeal to me as well. There is a lot of overlap in the sound of Symphonic Metal and Gothic Metal, but the bands I have labled as symphonic have all used full backing symphonies in at least some of their albums.
Learned my lesson there.
but you have a whole new world of music to explore!
What's not to be excited about??
and hostile 
some people got when they thought Elfboy was criticizing their favorite music. 
