Oh dear lord, I have too many op songs that I love to the point that I ended up just following a few bands. Examples of this are Naitomea/Nightmare (Death Note, Majin Tentei Nougami Neuro, CLaymore) Yousei Teikoku (Mirai Nikki, Ga-Rei: Zero) and Ali Project (Rozen Maiden, Linebarrels of Iron). Then again, I like my darkness a little bit? So warning, I'll probably have more heavy/loud openings in this post! Anime openings, imo, tend to set the pace of the anime in it's own way. If you have a really, really dark anime, if the opening is as dark and gloomy, then it gets you into the mindset of the series. Some animes tend to play this for laughs (Dokuro-chan anyone?) and some openings are damn cool, but just disapoint you about the series' content. But for example
which is Nobunagun's OP, is both fitting and unfitting. It's unfitting at first, but later it just... synchronizes super well with the entire series. I just love this op to death! Some really interesting openings are One Reason from Deadman Wonderland,
from Phantom ~ Requiem for the Phantom ~, Higurashi no Naku Koro Ni by the same titled series and a classic, Lilium from elfen lied. Each of these openings are powerful in their own way, and if not a bit mind bending once you realize what the series is about. I know there's so many more openings that I am skipping but jeez, there's just so many! I should compile a really big list, but these are the ones that just come off the top of my head because they mean so much to me and just connected me to the series so much that I loved it. As for EDs, I generally don't like many. Some are by the bands I've named above and those I tend to watch but... eeeeh. EDs tend to bore me 90% of the time. Although, speaking of emotionally tangling EDs, anyone that gets feels from Key (Angel Beats, Air, CLANNAD, Rewrite) will probably curse me right about now. Because always remember the Dangon Daikazoku!