Hopefully that title was enough warning. I'm mostly going to talk about romances, but that requires discussing some major plot events. Also swearing. It's memetic.
So, I've done Anders (friend), Fenris (rival), Merrill (first half friends, complete rival). I'm skipping Isabela completely. Sure, I've slept with her, but I can't bring myself to pursue a solo relationship with her.
Playing multiple paths means by necessity seeing characters from multiple angles, and that can really change how you feel about them. I'm glad I did Anders' romance first, because after what went down, I can barely bring myself to speak to him on further playthroughs, much less flirt with the guy.
First playthrough, I was totally on Anders' side. The Circle is an injustice! I let Bethany go to the circle, fulling expecting that we were going to stage a breakout and rescue her later. I fell hard and fast for the man who seemed to want me so desperately and was happily planning a revolution with him. I thought giving him the key to the underground passages seemed like a good idea. I would have been willing to start a war my way. I still don't see why that wasn't an option.
I got worried when he started being secretive. I suspected that he intended to blow himself up publicly - probably in front of the grand cleric, after asking for her help and not getting it - to bring attention to the plight of the mages, and was angry that he wouldn't tell me, but if that was his plan I could kinda understand why he wouldn't, and I couldn't entirely deny him the right to do it, even if it was obviously going to suck for me.
... So I was pretty pissed when it turned that instead he decided to murder innocent people, and had made me an unknowing accomplice. Goddammit Anders! I was willing to give you everything and this is how you treat me? But... it couldn't be fixed, and I'd come this far on a romance path, so shock and cognitive dissonance made my poor Hawke agree that everything was a-okay, she'd forgive him, they'd go on together.
I don't think she meant it.
Combined with defending Orsino only to find out what he'd done, and have him turn into a Harvester on her? I suspect my first Hawke completely snapped after the end of the game and strangled Anders in his sleep. At LEAST.
And it turns out that at least to me, when you're playing through and not romancing Anders? He's incredibly annoying. He whines constantly. That's all he is, just a scruffy shaggy pile of WHAT ABOUT THE MAGES? Yes, there are reasons, and he's aware that he's turning into nothing but the cause, but it's still pretty obnoxious to have around. (Also, I'm annoyed that if he kills someone in Act 2 and you throw him out of the party, the text gives the impression that he left town, but he's apparently still hanging around being buddy-buddy with Varric. I really think that cutscene should be altered if you've told him to get lost.)
Every subsequent ending, I've stabbed Anders, and felt like that fate was too good for him. I find it crazily unebelievable that other NPCs simply walk away and leave him to me, too.
Compare this to Fenris. I took a hands-off approach with him the first time, earning rivalry points, obviously, but being respectful enough to him that I never hit full rivalry. He killed his sister (on later plays I stopped him but the first time I left him to it), and turned on me in the final battle, and I had to kill him. But that didn't make me lose respect for him, especially considering how guilty I felt about the side I'd ended up on. Also, he was always polite about Bethany, and while he did have a bone to pick with Merrill and Anders, he was right. The rivalmance is hot, and very squee at the end (he has the best pre-final-battle romance dialog of anyone afaik).
And on subsequent playthroughs, spending time with him without Anders around to piss him off, he turns out to actually have a sense of humor and to be quite willing to accept a mage Hawke, even though his reasons for being paranoid are better than Anders'. He gets more lovable as I spend more time with him, not less.
Merrill... sigh. I got the impression she had the hots for Hawke even when I wasn't romancing her, but I can't see that relationship ever working out. I don't think she plans ahead well (no surprise!) She jumps in because she's got a crush, then declares love and forces you to either say you'll do anything for her or dump her completely. But what would she do then? Especially on a rivalmance path? I can buy her friendship romance, sort of. Rivalmance M looks like she'd be utterly miserable with Hawke and I can't imagine they'd stay together. It's not just her people she's giving up, since a rival Hawke would logically try to stop her doing more magic. Little Merrill with nothing to do but sit uncomfortably in a rich house with hard floors? Especially if Hawke's ruling the city and everyone's staring at the freaky elf? Eventually she'd run, or do something crazy.
This is getting super-long so I should probably split Isabela into the next post.