Lacuna Coil nowadays is mainstream alternative rock, have been going down that route for a while although their latest album Karmacode (or should I say KoRnacode) was the transition from metal to their current style. Whatever gothic metal elements they had disappeared after their debut "In A Reverie".
The Media and Mainstream Market has a very loose definition for metal and pretty much categorizes everything "heavy" or "aggressive" as metal. This however does not work as most people that are really into metal will tell you that Metal does not have to be heavy, or aggressive (Opeth - Damnation is a good example of this).
Some Rock (especially Grunge), some Jazz/Fusion, Punk/Crust (yes, the real stuff), Hardcore and 'nu-metal' *can be* heavier and more aggressive than metal.
Bands such as Slipknot, Static-X and all of the music on the Queen of the Damned soundtrack is not actually metal. Neither is Otep nor Devil Driver.
While the media and mainstream markets may misplace this music as metal, The term 'nu-metal' has been derived for this music by such markets. While the music itself may have some metallic elements incorporated into the sound, and in the odd places some metal drumming, it is primarily made up of Hardcore & Punk mixed with Alternative Rock and Post-Grunge with Thrash Metal influences (and in some cases, Hip-Hop and Rap vocals) (which is why I believe it should not be lumped in as a metal genre).
Also nowadays, "newschool metalcore" keeps getting called Thrash Metal for some reason, Thrash metal fans themselves would find this particularly appauling as newschool metalcore is a bastardization of both the oldschool Punk & Hardcore elements and ideals as well as Metal elements and ideals.
Trivium and most other metalcore bands are not Thrash Metal, however their metal elements are mostly borrowed from Thrash Metal anyway, but there are various stylistical and sonic differences, and a slight difference in the deliverance style of the music.
I'm not attacking anyone's opinion here, I am simply stating my own beliefs which I have accumilated through interest, research and my perceptions of the music & availible information on the topic. There are many different views and ideologies of metal out there, and as you[size=xx-small](pl)[/size] have probably seen displayed by other members of this forum.
Some things to learn & listen for when determining whether a band is metal.
*Metal is NOT a subgenre of Rock Music.
*The difference between the drumming styles used in Rock, Metal and Punk/Hardcore (as stylistically, metal came from a mixture of Jazz, Blues, Classical and European Folk)
*The differences between the guitar riffs/chords used in Metal, Rock and Punk/Hardcore (same reason as above)
*The idelological/musically political differences between the styles (this is a big hint against nu-metal and metalcore not being metal)
There is good music to be found in all of these genres/styles of music, and while I may not be a fan of hardcore, nu-metal and the like due to the ideologies and themes portrayed as well as finding sonic discomfort with the music, my opinion on this matter will be very strict and I will have absolutely no problem stepping in and pointing out the differences (which I believe some might find annoying).
However it was as a music lover, not a music hater, that I strived to learn this information, for a greater understanding of the music I am listening to.